You're effectively taking the position of "fuck the business for trying to survive". Amazon makes billions, why didn't they just pay the 30%? Because their margins are 5% at best. Survival. Not even wealth.
And the argument you're making can ONLY be used to support the position that "well then why isn't Apple just the only company in the world and everyone is forced by law to use them?" Because that's the long-term outcome of the thinking you are describing.
People have options, people want options. One of the things Apple does is refuse to allow developers to use specific banks to receive payments! So now they get to tell people what bank to use? And the bigger they get, the bigger they will bully themselves into literally every market decision on the planet. Oh but it's all OK because it's a closed platform.
Bully for you that your experience with Apple/In-App payments has turned out well, but the companies I work with ABSOLUTELY HATE THEM. Customer service, when it is necessary, is absolutely impossible. Refunding pro-rated amounts is also impossible, which means they're forced to refund all or nothing - and Apple still keeps its cut.
Mobile devices are used now more than websites, so mobile presence is REQUIRED for survival. This has given the two monopolies, Apple and Google, alot more power than frankly they deserve.