This one is a bigger issue. One of the projects I used to contribute to moved to Gitlab, and saw a significant decrease in organic contributors. GitHub simply has more users, better SEO, and a better ecosystem
GitHub has been recognized as harmful to the free software community at least as early as 2015, years before the Microsoft acquisition. See RMS email on GitHub.
GitHub allows you to select any license (including a proprietary license) or no license at all. This does not mean that GitHub encourages one to select a free software license or any license at all.
Anti-copyleft bias noted by Stallman and Sullivan is evident from the very beginning, from the founder Tom Preston-Werner himself. In 2011, Preston-Werner wrote that one should "open source (almost) everything" under a permissive license, because the GPL is "too dogmatic," but keep "anything that represents business value" proprietary.