You can host your own on your own site. Most major open source projects have their own website anyhow. They really don't need to be on github or gitlab to begin

You can host your own on your own site. Most major open source projects have their own website anyhow. They really don't need to be on github or gitlab to begin with, just roll it yourself like the rest of your website. The only reason why people do it is because its a meme at this point to have a github (and even gitlab, if only as a foil to github).