This is entirely on the companies. There's no technical reason or requirement for this happening.

Fdroid works great and is the most likely thing to be adopted, in my opinion. It's easy enough for anyone to spin up their own fdroid server and distribute their own app.

If you're wanting to use a new store, you're going to have to wade through the growing pains of adoption. It's just a fact of life.

Wait, I assume if you install a banking app through Aurora it still works? Totally fair if that doesn't work for your needs (you kinda need a google account, even if a blank one, to have it work right now) but I assume installing apps through it doesn't limit them or make them less functional for having been installed through Aurora?