I'm saying in a competitive market, the incentive would be to support as many platforms as you reasonably can. Without being outright paid by platform creators not to do that, most developers choose to do that. Paying third parties not to support your competition is... I'll let the reader fill in the blank :)

So instead of paying third parties they could just outright acquire them - like MS did with Bungie? At least independent game makers have the option of creating some games that are cross platform.

On the other hand, if the game maker needs funding and the platform owner is willing to fund them, shouldn’t the platform owner get something?

Another example, Apple funding independent game makers for Apple Arcade means that games can come to iOS that don’t depend on loot boxes, selling consumables or ads. That also means Apple takes on the risk.