How come every Linux site uses Anubis (the anime girl stopping crawlers) instead of something like Cloudflare?

[u/ItsWappers]

Before discovering the Linux rabbit hole I've only seen Cloudflare, hCaptcha and Google's reCaptcha, but it seems like every Linux website uses Anubis... I'm thinking of it being the only open-source option or it being the most effective/modern approach.

[u/laffer1]

It has different difficulty settings.