Hi @jfrankl8.
Perhaps, but that is how it works. There is no way around it.
This is not anything specific to the arduino/library-registry project. A GitHub account is required in order to contribute directly to any repository maintained on GitHub, just as a GitLab account is required in order to do the same with a repository maintained on GitLab.com. Although the open core nature of the GitLab service is laudable, the unavoidable fact is that far more collaboration on open source is done on GitHub. So I think that any but the most stubborn software developer will eventually find the need to create a GitHub account even if their own projects are exclusively hosted on GitLab.com. So you will likely find the GitHub account useful for more than just submitting your libraries to the Library Manager registry.