Rashi says on perek 11 pusuk 18 that you should keep the mitzvos in Chutz L'aretz, to put on T'filin and put up Mizuzos, so when you return to Israel you'll be used to it.
This would be understood to mean that in essence, mitzvos are only really in Eretz Yisroel, you only got to do it outside of Israel just for practice. (see Ramban that says there is a big Yesod in this Medresh). How can we understand the simple explanation to the Medresh, since simply aMitzvah that is not dependent on the ground of Israel, is an obligation for everybody "on their body" (i.e. a personal obligation) and not dependent on where he is at the time.
In my Humble opinion you can answer, the gemarah Shabbos 88A says that Hashem hovered Mount Saini over the jews and forced them to receive the torah, and there was a complaint on the torah untill the times of Achashverosh, then the jews took upon themselves the torah with love . The commentaries ask why did Hashem need to force the Jews, didn't they say "Naseh V'nishma" (We'll do the Torah before we hear it (i.e. we don't need to hear it to aprove of it))?
One answer they give that they only accepted only on condition that they have Israel, but if they went into Gulus (exile) then they don't want to keep it. That's why they neede to be forced. Thus by the giving of the Torah, there wasn't a strong obligation to keep Mitzvos outside Israel, thus they needed the reason to do it antways so you'll be used to it when you return. But now, after the miracle of purim, since the jews accepted the torah in all places, the obligation outside Israel is the same as inside.

Another answer could be, that we are talking only of the mitzvos that RAshi quotes and are in the Parsha, T'filin and Mizuzos. Part of the mitzva is to do something that will increase your life. The gemorah in Kidushin says the reason how we know women are obligated in mezuza because "they also need life". The gemarah Berochos 8A says that this which it says "in order to lengthen your days" by the above mitzvos, are only "On the land" but in Chutz L'aretz no. So in Chutz L'aretz, since you can't have the "in order to lengthen your days" the torah shouldn't have obligated you to keep it, so you need the reason that you should be used to it when you return to Israel.

This message has been edited. Last edited by: Rav Chaim,

I would like to add that, acccording to my first answer, that Klal Yisrael didn't accept the torah for when they weren't in Israel, this what Chazal says that Hashem told Moshe before he died, that the only reason you want to go in Israel to receive the reward of doing Mitzvos that are dependent in the land (so I'll give you reward as if you did it). Really he should want to go in to keep all the Mitzvos, since the real obligation is in Israel.
Maybe you can say that Yisrael as a whole didn't accept the torah in all cases, but Moshe himself, who was Hashem's middleman to try to "sell" the torah, accepted it in fully, so he was obligated in the Mitzvos even outside of Israel.
This would also answer why by the Golden Calf , Moshe told Hashem that he only commanded him not to worship idols (since those commandments were written in the singular.) According to this, it is not only a question of linguistics, but that Moshe was the only one that accepted the torah in all places, hence in the wilderness he's the only one that can be held accountable for it.

How is it possible to say that the Jewish people before Purim were not fully obligated to keep the Mitzvos outside of Eretz Yisroel because they were not willing to accept that, when we see Hashem forced them to do just that when he held the mountain over their heads?

What I wrote about outside Eretz Yisrael that the obligation wasn't as great was from the Koseiv in the Eyn Yaakov in the name of the Rashba. What forced him to make the difference between Israel and outside was for this point: how could Klal Yisroel be punished for the Aveiros (sins) they did before the Purim story, since they weren't obligated. Thus he says that they where punished for what they did in Eretz Yisroel, and there was only a limited time between the exile and Purim, ther wasn't much you can prove that they were punished for that time.

If so, if accepting by force is not considered accepting, and is not obligate, why then did it help to force them? (which the flip side, if they need to accept hte torah, how could you force it on them?) This is a good and I would like to think it over before I give an answer (I'm thinking of an explanation, but I need to get it clear, and besides, my wife wants me to do the dishes now

I think I have a good way to explain it (it's better than the way I did the dishes .)

There is a gemarah in Baba Basra that says that if someone forces someone else to sell him something, the transaction is good, and it's halachacly sold (even though it is prohibited to do so). Since he is forced to sell, and he's getting the money for it, we assume that the average person will decide to accept the payment as good and complete the sale. If forced to give a gift, the gift does not Halachicly go through and you can get the gift back by bringing him to court.

The gemarah compares forcing a husband to divorce his wife (in the case where the Rabbis decided he should divorce his wife) or to bring a sacrifice that he's obligated in to forcing to sell. Tosfos explains the reason why it's considered like the sale and not the gift, since he has an obligation to divorce or to bring the sacrifice, he's receiving the fulfillment of his obligation as receivement of payment.

When the jews accepted the Torah in Israel, then part of the obligation is to keep it in chutz L'aretz so that you're in shape for when you return to Israel. Therefore, when Hashem forced them to accept the torah in all places, it's like forcing to sell, since they're anyhow obligated to keep it there in order to be in shape to keep it on their return.

The reason they must accept the torah completely in all places, and it's not good enough to keep it to be ready to return to Israel, because the jews receiving the torah was their conversion (In Yevomos the gemarah learns halachos of conversion from how they received the torah.) If they wouldn't accept the whole torah they wouldn't have done a full conversion, thus Hashem had to force them to accept all the torah.

The difference is that once they were forced to accept, they can't be held responsible for the torah, only as much they would been held accountable as if they only needed to keep them to keep in shape for the return to Israel. For the extra punishment that would apply to the regular torah over the punishment for keeping them for the return, would be like forcing to give a gift , since they are not obligated anyhow in the extra punishment, so they couldn't be punished that much.

I am not sure what you have gained with all of this. You are back to the original question as to why would mitzvos performed in chutz l'learetz be only for practice seeing as they are not dependent on the land.

since the Jews never accepted the Torah from their own free will in chutz l'aretz, even though the Torah requires these Mitzvos to be done in chutz l'aretz, but they never accepted that. Thus their whole obligation in chutz l'aretz was only to do it as a practice, because more than that they just never accepted to do under free will.
So once they must do it anyhow for practice, so Hashem can force them to keep it for the regular obligation of the torah, but they can't be punished only for what they accepted thru free will, which is as a practice

once the bnei Yisroel were willing to accept the mitzvos,what would be their motivation in only wanting to do them for practice? As long as they are doing it ,why not for real reason?

The difference is in the punishment. If somebody would do work on Shabbos in Chutz l'aretz, if they would accept it for the Torah alone, they would receive death for doing it on purpose and must bring a Chatos if done unwittingly. But if it's only as a practice, it might just be just like transgressing a positive commandment or less.