The amount of downtime, sudden server crash, problem with SSL with NAT, setting up gitlab runner, upgrading, etc. You'll need someone experienced enough and maybe even a dedicated infra role to handle those things
Same story for the primary free software project we rely on (who we have a support contract with). Neither us nor them spend anywhere close to 10 hours a year on maintaining selfhosted Gitlab related infrastructure.
People underestimate consistently how complicated is to build reliable things, hardware or software. There is a world between "it works for me" and "it works for all"
Reasoning was if the file server was down, it would come back up quickly because it affects everyone. I didn't understand this reasoning until I got emails from the database team saying the database servers stopped working and every development team now needs to change their connection string from machinename-abc.corp to machinename-bcd.corp
How in the world someone could write an email like that is beyond me. Ok machines crash all the time but why can't they reuse the same name for the new machine?
(And that's literally only because I choose to update it manually since it's usually offline for about 15-30 minutes during updates...)
Depends on where you are are doing it. AWS makes it ridiculously easy to hand off basically all aspects of hosting. Set up once, use forever.