If 3rd party stores didn't charge the Apple tax, I think you'd find plenty of apps moving to other stores, and within a matter of weeks more than half of users would have used a 3rd party store.
I want the equivalent of a shops in the real world. One shop doesn't carry everything. Even Spotify doesn't carry everything. For one, Apple doesn't allow adult content apps. Steam does. I'm sure there's a market for adult games on iPhone as Steam's success there would seem to suggest. I don't think Apple should be required to sell adult games but I also don't think they should get to dictate that people can't use their phones for adult games. So, more stores would great.
Yeah but these companies will force me to install their garbage third party app stores to install their apps. I really just want one good, properly vetted app store on my phone, is that so hard to understand?
If you ever tried out third party app stores on Android you’ll see what I mean. See also the crappy launchers/stores major game publishers try to force on you on PCs.