I suspect you're just repeating arguments you've heard, so don't take this internet rage personally, but that is complete bullshit.

• Hosting costs nothing. Devs will gladly foot the bill for that if given the option. Even if you distribute your apps on AWS (which is notorious for severely overcharging on egress), your expenses will be no where near 15%-30% of your revenue.

• Payment processing is a competitive field outside the appstores. Even 15%-30% is ludicrous when "overpriced" processors like stripe charge 2%-3%

• APIs are not something sold to developers. They build them as part of the operating system because they have to. That's how it works. They could try selling licenses, but it would result in devs not building on their fancy new features.

(you didn't mention the ones below, but people with your argument usually do, so I'm adding them for completeness)

• Security is also bullshit. The Appstore and Play store are FILLED with malware. It is not physically possible to manually review the sheer volume of apps published to those stores. They also are not incentivized to improve the process much, because each time your kid or grandma accidentally activates a $40/week subscription, Apple/Google take a 15%-30% cut.

• Curation/promotion is bullshit. Discoverability on these stores has always been bad, but has been particularly awful since both Apple/Google have started selling search ads in the store. The other day I almost accidentally downloaded a fake ChatGPT app because it was the first result when I searched, it had a very similar icon, "ChatGPT" in the name, 5 stars, and millions of downloads.

These stores also heavily incentivize devs to push subscriptions. I suspect (but haven't confirmed) that the Appstore and Google Play both rank subscription based apps higher than others, and subs tend to pay a lower revshare fee than other monetization types.

I could go on all day about the rotten dumpster fires that are these disgusting stores. The only people who defend them are fanboys and people who have never actually had to deal with them professionally.