Just joined a company that self hosts Gitlab (and everything else, there's zero cloud) but is 100% remote. So far everything has been seamless and there's a large enough infra team to solve these issues if they arise :)
And it's definitely possible to run gitlab or any other git hosting solution on-site with little downtime. There's no magic or arcane knowledge involved. It just takes serious effort to do so - more than a single lone wolf sysadmin can provide. All their skills are worth nothing if they're sick and in hospital or on a beach holiday.
Maybe, but also maybe not. And then that still doesn't mean I want them to focus on running git/gitlab. I mean we're doing stuff that revolves around the rust compiler and we have operations people easily capable of running gitlab around, but their primary task is something else - they're building systems on top of that. Do I want to re-task - or even just side-track them - into running gitlab?
Once you reach a certain size, you can have an internal ops team that's responsible for providing internal infrastructure, but to what extend is that really different from giving github/gitlab money? They'll be about as far removed from the individual teams they're serving as github is. Is that really something I want to put organizational effort into, distracting the org from achieving the goal? It's all tradeoffs.