> 30% became the industry standard not just for video games for a reason.

Yeah, it became the industry standard because it rakes in mind-blowingly huge revenue for the app store owner, e.g. https://www.cultofmac.com/601492/app-store-google-play-reven.... From the article: "It’s no wonder Services — which includes App Store revenue — has become an increasingly important business for Apple as hardware sales have slowed.".

While you're correct that it costs money to run Steam, it's not _that_ much money.