Control. It allows them to control the speed of progression by breaking its relationship to time investment. That way they can keep us mindlessly grinding for item level via RNG. So we don’t notice how little loot this game actually has to offer.

Its a deliberate bottleneck to progression to stretch out the grind. As I stated in my post, the most insidious aspect of this is the limit of 20 ghost fragments which isnt enough to buy all of Spider's bounties. It is deliberate layers upon layers of bottlenecking. They have turned leveling into a chore as opposed to it being organic.

Artificially inflated grind because they know for a fact that this content isn't anywhere near as replayable as destiny 1 was.