It just has a very large loot table. If you are past the point of needed those legendaries you are at the end game for sure. It's not like nightfalls are hard. You don't even have to start over anymore.
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Being past the point on needing 270-280 legendaries doesn't mean you are end game. Heck 270 is 10 lower than recommended for the nightfall 280 is recommended. Rewards should be higher than that.