The Torah states that Reuven and Gad chose to live on the other side of the Yarden because it was ideal for grazing livestock, which they owned in abundance. Why, in Ve'zos ha'Berachah Devarim, 33:21 does the Torah not mention this reason?
Rashi (in Devarim 33:21): Because they wanted to reside in the area where they knew that Moshe Rabeinu was destined to be buried 1 - and perhaps that was the main reason for their choice 2 and they only used the argument of shepherding their livestock in order to present a united front together with Reuven.
He was buried in Gad's portion. (Refer to 32:38:151:1). We do not find however, that Gad requested a share in Eiver ha'Yarden containing his grave. Perhaps we can extrapolate from there that they did! Or, Gad initially asked for Eiver ha'Yarden, hoping to get all of it, but then Reuven joined them,due to the excellent-quality pasture-land. (Perhaps Gad attributed their request to pasture, in honor of Moshe who still hoped to enter Eretz Yisrael. Alternatively, they merely wanted to be on the same side of the Yarden as his Kever. In any case, they cannot visit it, for no one knows where it is (Devarim 34:6)! (PF) Da'as Zekenim (Devarim 33:21) - since they knew that Moshe would be buried there, they did not fear Amon and Mo'av's claim to take it back. Hashem would not bury him in Chutz la'Aretz! B'chor Shor (Devarim 33:21) - also, they wanted Moshe's merit to protect them.
Perhaps that will also explains why Targum Yonasan translates 'N'vo' as 'Beis Kevurtei de'Moshe'.
What was Moshe accusing Gad and Reuven of?
Rashi: He was accusing them of putting fear into the hearts of the other tribes, 1 who would think that they were afraid of crossing the Yarden to fight the Cana'anim.
Ramban (in Pasuk 2): He was accusing them of a lack of Bitachon like their fathers, 2 as a result of which they were afraid of the Cana'anim and did not want to cross the Yarden. 3
Seforno (in Pasuk 6): He asked them whether they really thought that their brothers would agree to cross the Yarden to conquer the land whilst they remain in Eiver h'Yarden - knowing full-well from the previous generation how those who turned others away were punished.
Targum Yonasan: He accused them of negating the other tribe? motivation to cross the Yarden to enter Eretz Yisrael.
Even though they themselves were not necessarily afraid.
Ramban: As the Meraglim said in Sl'ach L'cha, 13:31 "Lo Nuchal La'alos el ha'Am, ki Chazak hu Mimenu!"
Ramban: And this in turn, would result in their having to remain in the desert a second time (As implied in Pasuk 15 - See Targum Onkelos and Targum Yonasan there).
