I've done a few apps as part of my day job. And my best explanation and/or analogy is government regulations. The store requirements, apis and rules are documented up to the upteenth degree in 49 pages spread across many areas, and unless you're "in the know", you have no way to implement it to a reliable degree. And then all this ends up doing is punishing small / low-budget / low-time developers, leading to consolidation around the big players.
The big players can push their weight around to some degree, they get an element of built-in trust, and they have the sheer budget/time to implement all the ridiculous and sometimes onerous requirements. All in all, they're cementing their market position and trying to make "sticky" and invested players that will prop-up the play store for the coming decades.