The Fandom Menace strikes again.
But seriously, this is messed up. People need to learn to treat others with respect and kindness. Hopefully the maintainer is able to simply move on after archiving the repo, and isn't dealing with any mental struggles from dealing with years of entitled users demanding things for free.
In popular open source projects this is a recurring issue. I suspect the only way to deal with it is to either shift to a platform that has better tools for moderation, or end the project like the maintainer has done. Let someone else fork it and deal with the users.
To clason: Thank you for all the work you did maintaining nvim-treesitter!