@sam@r1b.it I think a lot of it boils down to knowledge. You'd be surprised by the amount of people who need their hands held the first time they buy a domain name, who have never so much as paid for a subscription to a managed service before.
It's easy to take for granted the technical abilities that are necessary to self-host an instance. None of it is exactly difficult, but it's time-consuming and requires a lot of specific knowledge.
@Auster@thebrainbin.org Bookwyrm and NeoDB are both awesome alternatives to GoodReads, with NeoDB offering far more than just books.
The only downside is that Kindle directly integrates with GoodReads, I'm not sure there's been any independent efforts to integrate alternatives into e-readers.