I actually am surprised that services like Steam, the Apple App Store, and Google Play are able to command as high a margin as they do for sales commission. I mean, it's obviously possible because it's reality, but it's nonintuitive. I wonder if it will continue to be that way. For iOS, you don't really have a way to install apps outside the app store without jailbreaking, but you do for macOS, and I've seen a number…
Collecting money is an important part of a business, but also not trivial. It therefore makes sense that people would outsource this. If you get big enough, you probably don't want a middleman in the way; this is why companies like Blizzard have their own store/launcher app. For everyone else, whatever they take is cheaper than having their own army of software engineers, lawyers, billing phone support, etc. In a wor…
This completely misses the value proposition of Steam. Collecting a million dollars of game sales through Stripe or PayPal is not hard, nor is dealing with payment issues a large overhead, even if you're paying the people replying to the emails programmer salaries.
Supporting the game itself is an order of magnitude greater even if it's decently written. Steam doesn't prevent that support, it just obfuscates the customer's connection to you so if you don't care you can mostly get away with ignoring them (at your peril, as it will invite bad reviews).
Steam puts you in touch with an immense audience. That's the value they're bringing to the table, and it's a big one.