I think it’s also a chicken-or-egg question:

Apple users are more willing to pay for apps. So if you’re a dev and you want to release a paid app, iOS is the platform of choice. So more devs release paid apps on iOS, so iOS becomes the platform with more paid apps. So users are more used to pay for apps. So paying for apps is normalized, so Apple users are more willing to pay for apps.

Etc. etc. etc.