Github dislikes email “aliases” so much that they will shadow ban your otherwise normal activities for months, and once flagged, support will request not only a “valid” email domain but also that you remove the “alias” email from the account completely.
Sure, self-hosting is a great option for very large projects, but a random python library to help with an analytics workflow isn’t going to self-host. Those projects, along with 27,999,990 others have chosen GitHub, often times explicitly to reduce the barrier to contribution.
Also, all of those examples are built on thousands of other FOSS projects, 99% of which aren’t self-hosting. This is the same as arguing only Amazon is a bookseller and ignoring the thousands of independent book publishers creating the books Amazon is selling.
This isn’t to say every project should self-host, but that they could self-host. And if you don’t want to self-host, you can join groups like Notabug, or a server hosted by a foundation like Codeberg, or the privately-held SourceHut, or even the open-core GitLab with its free tier (tho publicly-traded, most of the source is open & one can run the community edition if they wish). To assume if not self-hosted GitLab CE, then one must use a closed-source, US-based, publicly-traded, megacorporate, social media + code forge platform that’s trying to monopolize the developer tooling space is a false dichotomy.