It seems like a useful privacy feature to me. I don't want Apple or Firefox to pass every site I visit every time I visit it to Google, Apple or any other company under US law.
Firefox on Android e.g. used to (or still has – I'm not sure what the state is nowadays after the rewrite) have a similar (although somewhat smaller) list of popular domains which it would use for providing autocomplete results if it couldn't find anything in your history, but local history always had priority.
Joking aside - Firefox makes some strange choices and the I wish mobile and desktop could (optionally) share more of my browsing history. Maybe they do but the autocomplete doesn't behave the same across devices.