Creating a GitHub repo with one file titled “index.md” and publishing it to GitHub Pages creates a single-page site using relatively sane defaults. There's no maintenance involved whatsoever. You can add multiple pages as well by creating new .md files and publishing them.
No, GitHub pages are tied to "an" account. It can be a secondary "anonymous" account. You can create an anonymous bear blog or one of the other million free writing and zero maintenance tools. It's certainly more anonymous than having to disclose your real identity via a credit card on a random person's page.
Also, what sort of content do you hope that your target audience (Bob the landscaper who is non technical but has a super urgent desire to send a message to the world in an anonymous way) will publish?
Yeah but would I tell my mom to pay a dollar on this site? Would she trust it? Does she need a website or does an email/google doc satisfy her needs. What are the use cases for entirely anonymous sites that you have in mind?