aurora store currently supports aab file format.
go to an app's "more about app" section and scroll to files section. you can see bunch of apk if app is using aab.
because platforms need development tools for developers.
browsers has "developer tools" and android has "developer tools and adb".
standart users doesn't use adb or development tools but they still inside an android system. sometimes seperate builds for user and developer is not nice solution.
( i'm living with $500 in izmir and my rent is $120 )