The real reason you shouldn't be using GitLab is performance. How is it possible that that page took over a minute to load? Nevermind that the design is completely incomprehensible.
I make a habit out of pushing to both gitlab and github. Even if github is technically superior, I don't think we're served well in the long run by monocultures.
(But yes, gitlab's web interfaces are generally frustrating. Slow, bugged, or just organized in ways I find challenging.)
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.
