GNU grades hosting services based on different sets of criteria. GitLab gets a C, "acceptable hosting for a GNU package", but not "good enough to recommend" because the JavaScript on the website is free but doesn't work with analyzers like LibreJS, and because GitLab doesn't discourage bad licensing practices. GNU Savannah, of course, gets an A.
Things that prevent GitLab from moving up to the next grade, B:
All JavaScript code served to the client is free, but does not work with LibreJS enabled. (B0)
Encourages bad licensing practice, including no license; failure to state the license on each source file; and failure to say which GPL versions apply. (B2)
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I think at least B2 is a reasonable request, although this may have already been fixed (sorry, I use gitlab but barely visit the site itself).
You are correct. To avoid a common misunderstanding I'd like to note that GNU people have no problem using software that has been released under the Expat license. It doesn't have to be copyleft software to be free/libre.
Why don't they use GitLab CE? It's under the GPL