Why do you need a "most" qualifier?
Yes, companies continue to put money into things that continue to make money. Nobody has ever claimed that the entirety of that revenue goes back into ongoing development, and I don't know why anyone would expect that to happen, or have assumptions about 'how much' of that revenue goes back into ongoing development.
Because it doesn't matter. Its none of your business unless you are a shareholder.
As a consumer, do you get ongoing development for free funded by mtx? If yes, then case closed.
It really doesn't matter if its 1% of the revenue made or 99% of the revenue made, you are getting ongoing development paid for by MTX.