1. most open source software is not even
close to breaking even via donations. so "making more money" really is a misleading way to portrait the situation.
2. I hope we can agree that "if you use their store as a sales funnel then they take a 30% cut" is at least a
use of their power. The fact that there's no recourse, no (practical) competition for the distribution, and that they're not acting in agreement with their "official" stance on free-as-in-beer or free-as-in-speech software makes it an
abuse in my book. The thing is, they don't officially say "we only host apps that make
us money, not at all. They say they're just platforms, facilitating exchange, blabla. Also, see point 1: "sales funnel" for projects that maybe (!) manage to break even on their hosting costs is not the right term to use here.
This is an old claim by now, but these platforms matter a lot today, and since we only have two of them, and they are not in direct competition (users cannot switch at will) they really should be treated as the monopoly infrastructure that they are. What that means concretely is subject to negotiation within society.
In my opinion blackmailing the devs of an application that is essentially written and maintained as a service to the public, for free, by volunteers, is a shit move to say the least.