> why the developer would bother with their own store if the App Store now allows emulators
The keyword is now allows emulators. They didn't allow it 3 weeks ago. Or a year ago. Or 10 years ago.
Only now, with alternative stores launching and offering this, Apple has finally allowed emulators.
Perhaps the developer doesn't want to be beholden to Apple's whims? Especially after investing a lot of effort into setting up an alternative store?