No, of course it's not surprising that they're not a charity. Sure, the big app stores exploit their near-monopolies with exorbitant fees.
Good for Apple, Valve and Google, but I think it's better that game dev studios and app developers get money instead. However, devs don't currently have a real choice but to pay up.
Competition can change that, so we should support technically worse stores like Epic so developers will not have to pay their unreasonably high fees.
Are you not aware that public companies split the profits too? They do not need to grow to have value for investors.