Or competition.

Or that more reviewers might lead to more apps which lead to more revenue.

Competition would have to come in the form of regulation given the lack of other options on iOS

I suspect Apple knows that most of their revenue comes from the top 500 casino games for children. They probably get all their reviews fast-tracked to keep them happy.

Most (by quantity) of the rest is apps that are free and don't make much money from IAP and just monetize with tons of ads. Apple doesn't get their beak wet on those so they know that even a few million more spent on reviewers wouldn't make a big difference in their own revenue.

The rest of us, we just have to wait our turn.