Tech illiterate people are barely installing new apps on their phones, let alone separate app stores. Almost everyone I know runs Android and I've never seen F-Droid or Aurora or any other alternative app store on their phones.

Scammers can already trick your mother into installing their apps. https://altstore.io/ exists and is widely used to install an emulator and some other apps Apple has deemed unworthy of their users' attention. The source is here: https://github.com/altstoreio/AltStore