I think a lot of people come to Nix and NixOS from Linux and similar environments, where having "repositories" or "registries" is fairly common as a way for distributing indexes of software in their distributions. So it's quite naturally moving in that way.
But for someone coming from OSX/macOS or Windows where there basically is just one index (provided by the companies maintaining the OSes) and you can't really add/remove others, it's a completely new concept, makes sense there is at least a bit of friction as those people wrap their head around it.
I'm not sure I understand your point. You're saying that channels are like apt/sources.list or yum.repos.d, and flakes are like the Apple App Store? Or the other way around?
One thing that probably didn't help my understanding of channels was that I run Nix on non-NixOS systems (primarily MacOS and Fedora). If I'd stuck to NixOS, then thinking of a channel in the same terms as apt/sources.list or yum.repos.d would have been an easier mental model.
But for someone coming from OSX/macOS or Windows where there basically is just one index (provided by the companies maintaining the OSes) and you can't really add/remove others, it's a completely new concept, makes sense there is at least a bit of friction as those people wrap their head around it.