Apple and Google's 30% not only hits the base price, but every single transaction that happens inside apps as well. Imagine a toll bridge in front of your nearest supermarket where the people working the toll booth inspect every bag of grocery you bought and then charged you toll based on what you bought there.

Apps arent entirely like video games. If you wanted to open a non-subscription based music store or book store or whatever, you'd find it economically impossible to pay the publishers their cut, apple their cut, your server host their cut, and have anything left over for yourself without charging your customers their arms and legs. This is why all those kinds of apps are subscription based. You can cleverly batch and bundle stuff in a monthly subscription fee which gives you room to dance around google and apples high fees and have enough money to keep your lights on.