There only seems to be a double standard because you're making an invalid comparison.

On most smartphones, while there's a high bar to pass to get into the official "app store" for that phone or service, nobody is stopping you from selling an app outside that store. As such, Apple's review process is not merely a review process for a store, but also serves as a review process for all applications that a user can install on the phone.

It's the difference between a lengthy review process for selling a game on Steam (reasonable) and a review process for selling a game that a user can install on Windows (not reasonable).