Ramban: Because it was situated by the crossings of the Yarden, and it is from this point that they would eventually cross into Eretz Cana'an. ¹

Rashi #1: From here we see that Moshe coveted the same death as Aharon. ¹

Rashi #2: It is to inform him that, since it was decreed that both of them could not enter Eretz Yisrael because they had sinned by failing to sanctify Hashem's Name ² and Aharon had died in the desert, Moshe was no better than him, and he must therefore die too.

Rashi #1: To teach us that, had they sanctified Hashem's Name (by carrying out Hashem's command to the letter), their time to leave this world would not yet have arrived.

Rash #2: Because Moshe requested it, ¹ in case people think that they did not enter Eretz Yisrael due to a lack of Emunah, like the rest of the generation that left Egypt. ² The Torah therefore fulfilled his request, to let people know that this was their only sin. ³

Oznayim la'Torah #1: Either because it wss too far away or because, as opposed to Moshe, who pleaded with Hashem to enter the land - and whnose Tefilos were partially answered by allowing him at let to see it, Aharon did not Daven to enter it.

Oznayim la'Torah #2: Refer to 20:24:2:1.

Oznayim la'Torah #3: Becuse Aharon participated in the sin of the Golden Calf and was therefore subject to whatever punishment Yisrael was subject to - as Hashem stated there ¹ "u've'Yom Pokdi u'Fakadti". Perhaps that is aso why he was punished by the sin of Mei Merivah more heavily than Moshe.

Moshav Zekenim (in Devarim 3:27) and Riva (in Devarim 3:27): Moshe said, 'People will say that I am among [those who needed] the Meraglim, about whom it says "ve'Chol Mena'atzai Lo Yir'uhah" '. (14:23)! Hashem therefore told him that He would show it to him (to nullify this concern).

R. Bechayei (in Devarim 3:27): Moshe called Hashem "Elokei ha'Ruchos le'Chol Basar" (16:22). Through seeing all four directions of the land with an eye of flesh, Moshe would be able to contemplate Hashem's four-letter name, which is the first Merkavah for the four directions of the world.

Seforno (in Devarim 34:4): It was in order that he should bless it. ¹

Ner Uziel (p.215): Moshe's Midah is Netzach (eternity) Moshe looked at Eretz Yisrael to arouse a yearning for it, that lasts forever within Klal Yisrael even through thousands of years of exile.

Ramban: Refer to 27:12:2:1. This implies that, to the contrary, if he could not enter Eretz Yisrsel, at least he would have the satisfaction of seeing it. ²

One can safely assume that the joy of seeing what his beloved nation were about to inherit would override the pain at not being able to enter it himself.