If you sell an app on an alternative store, how do you get the average person to install it? Adjust your marketing materials to teach them how to find the hidden "allow unknown sources" toggle on their phone, and then say something like: "Just ignore the many scary warning messages telling you that you're about to get a virus, and implying that we're malicious. Also, don't let it scan us for malware, not because we're malware, but because Play Protect may end up accidentally blocking us, and we have no idea how to get that reversed".

And even if you do that and manage to get enough customers to qualify as a potential competitive threat, Google will put together a task force[1] to destroy you.

1: https://www.androidcentral.com/google-fortnite-task-force