Rebbi Simla'i's question must be rhetorical. It cannot be read as if he were making a serious analysis, taking a lomdisheh approach. If it were, it would make no sense at all, because his question is not much of a question. Considering the depth of our forefathers' desire to live, or if not to live, at least to be buried (Yaakov, Yosef), in the Land of Israel, Rebbi Simla'i shouldn't be wondering what Moshe Rabbeinu wanted. Certainly, what seems like sarcasm in Rebbi Simlai's question would be out of place. (The fruit he needed? To enjoy the pleasures he needed?) So we should read it as a rhetorical question, a pure Drasha, something intended to highlight the great value of Yishuv Eretz Yisrael: "Do you think he wanted to visit because he was looking forward to eating good food there??? Of course not! He wanted to immerse himself in the holiness of Eretz Yisrael."
(More evidence that Rebbi Simla'i didn't intend his words to be analyzed halachicly is the brouhaha among the poskim whether we ought to say the phrase "le'echol mipiryah v'lisbo'a mituva" in the bracha achrona of Al Hamichya.
The language of the Tur in 208:
and the Bach there says
Elsewhere we discussed an approach that this phrase, as used in this bracha, refers to the fruit of Bikkurim and Ma'aser Sheini, which are a mitzva to eat, since the fruit used for those mitzvos are the ones on which we say the bracha of Me'ein Shalosh.
But in any case, the Bach's pshat is more understandable if Rebbi Simla'i just wanted to highlight the great value of Yishuv Eretz Yisrael, and he used to words as a homiletic reference to physical pleasure.)
Having said this, the fact is that many people do take Rebbi Simlai at face value, and apply Gemara analysis to his words. Assuming that they are correct, we need a good pshat in what he means to ask.
The Geon Yaakov and the Satmerer (Vayoel Moshe, first piece in Va'eschanan, vol 8 page 39-42) and others have an approach based on the assumption that Moshe Rabbeinu knew that he would die on that day or the next and that he would be buried in Chutz La'aretz, so the experience of living in Eretz Yisrael would not be meaningful for him. This approach requires extensive re-alignment of Rebbi Simlai's words, and doesn't strike a chord with me.
Reb Meir Simcha (Devarim 11:33, first piece in Re'ei) mentions that Harav Dov Meizels also asks this question- that if, as some Rishonim (e.g., the Ramban,) dwelling in Eretz Yisrael is a mitzva, what's Rebbi Simla'i's question? Reb Meir Simcha answers that it was because Moshe was already on the east bank of the Jordan, and one who lives on the East bank also fulfilled the mitzva of living in Eretz Yisrael, that Rebbi Simla'i asked the question.
However, this would only be a pshat according to the Kaftor Va'Ferach and the Ramban, who hold that the special kedusha of Eretz Yisrael applies to the East Bank. According to the Tashbetz, it does not. So, again, we need a pshat in Rebbi Simla'i's question.
(Tthe Tashbetz holds that although the mitzva of living in Eretz Yisrael does apply to the East Bank (מצוות דירה/קדושת מצוות,) the special hashra'as Shechina (חיבוב דירה/קדושת שכינה) is only in the main body of Eretz Yisrael- the West Bank- and it existed even before the conquest. The Kaftor va'Ferach and the Ramban hold that not only does the mitzva to live there apply to the East Bank, but that the special kedusha applies there as well.)
I'd like to suggest some possibilities. As always, (in fact more than usual,) this is a vort in progress.
1. Kedushas Eretz Yisrael is essentially a means, not an end: it is a means of becoming closer to Hashem. Since Moshe Rabbeinu spoke to Hashem panim el panim, Eretz Yisrael had nothing to offer. This seems inconsistent with the expressed desire of the Avos to be buried in Eretz Yisrael.
(Update: Chaim B. points out that this could be better expressed as "that the din of Yishuv Eretz Yisrael is not a mitzva, it is a machshir. Since Moshe had achieved the goal of the hechsher, the din of Yishuv did not apply to him." Chaim also points out, essentially, that to say this is basically echoing Korach's argument that since the purpose of Tzitzis is to remind us about mitzvos, a person that already remembers the mitzvos has no mitzvah of Tzitzis.)
2. Before Eretz Yisrael was singled out via the entrance of the Bnei Yisrael, it was no different than any other land. For example, there is the Mechilta (Shmos 12:1) that says
ועד שלא נבחרה ארץ ישראל, היו כל הארצות כשרות לדברות, משנבחרה ארץ ישראל יצאו כל הארצות. עד שלא נבחרה ירושלים, היתה כל ארץ ישראל כשרה למבחות, משנבחרה ירושלים יצאת ארץ ישראל. שנאמר 'השמר לך פן תעלה עולותיך וכו' כי אם במקום אשר יבחר' [דברים יב']. עד שלא נבחר בית עולמים, הייתה ירושלים ראויה לשכינה, משנבנה בית עולמים יצאת ירושלים שנאמר (כי בחר ה בציון) ואומר 'זאת מנחתי עדי עד' [תהילים קלב]. עד שלא נבחר אהרן היו כל ישראל כשרים לכהונה,משנבחר אהרן יצאו כל ישראל שנאמר ' ברית מלח עולם היא לפני ה' '[במדבר יח'] ואומר 'והייתה לו ולזרעו אחריו' [שם כה']. עד שלא נבחר דוד היו כל ישראל כשרים למלכות, משנבחר דוד יצאו כל ישראל שנאמר 'הלא לכם לדעת כי ה' אלקי ישראל נתן את הממלכה לדוד' [דבה"י ב' יג'].
that until Eretz Yisrael was singled out, all lands were fit for prophecy (i.e., prophecy could take place in any other land,) but once it was chosen, no other land could have prophecy. So you see that only with the onset of Eretz Yisrael's special status, after it was conquered by the Jewish people, did it attain that special quality. But this is contradicted, again, by the obvious desire of the forefathers to live or be buried in Eretz Yisrael.
We could, however, deflect that criticism by suggesting that the forefathers wanted to be buried in Israel not because of its quality at the time of their death, but rather because of the inevitable change they knew was coming. As for their desire to live there, we don't have any pesukim that clearly state that fact.
Still, I'm not thrilled with this pshat.