I wouldn't say GitHub is nicer or more polished than GitLab. Both have similar feature set ( GitHub did well to catch up after years of stagnating, with Actions, docker/package repositories, etc) even if GitLab still has an advantage there, good ecosystems ( GitHub has more tools integrating with it than GitLab), and both work and are fully polished.
In the specific instance of GitHub, I have to agree it's nicer and better polished than the alternatives, but I'd also say the Free Software alternatives (GitLab, SourceHut, etc) are catching up, and are already usable. Hosting your own GitLab instance gives you a far nicer solution than an old school solution like SourceForge.
> we’re finding that a lot of things are just nicer because a large paid staff of engineers is working on it every day
People are paid to work on various Free and Open Source software projects, including Firefox and Notepad++, and most famously, the Linux kernel.