Performance and UI are valid considerations for using or not using any service, but not everyone has the same requirements on either of those.
If you don't find them acceptable, that's legit. Those are the "real reasons" you shouldn't use it. However, those reasons may not apply to others. They don't apply to me, for instance, and as Gitlab has a lot of users, I'm not alone.
If you don't find them acceptable, that's legit. Those are the "real reasons" you shouldn't use it. However, those reasons may not apply to others. They don't apply to me, for instance, and as Gitlab has a lot of users, I'm not alone.