As a developer I routinely compile projects that Apple has never seen and run them on my iOS devices. It’s not locked down in the sense that it’s impossible, but that the barrier is too high for normal users (who also don’t have a developer program membership).

Im Europe we have alternative app stores on iOS too.

But at the end of the day, even as a technically adept person, I don’t care that much about what my phone can do beyond the actual phone things, and just want it to be a reasonable smartphone that doesn’t need me to be technically adept just to be useable.