It's funny I see this comment all the time on HN, but in a very similar scenario recently, where DHH launched Hey app and was stonewalled by Apple, I didn't see a single comment saying "hey just go build your own app store". Telling someone to "just go build your own" is lazy and weightless.
I didn't find the subject interesting but I'll complete the request for consistency here: it doesn't bother me that Apple requires Hey to use in-app purchases.
"Just build your own web host" is feasible, but "just build your own app store" is not because it requires replacing half of your users' mobile phones.
No, it's not. Because eventually you get censored by domain registrars themselves. Not to mention DDoS mitigation providers, payment providers, browsers etc.