Cloudflare pages. The only real limit on the free plan is "500 builds / month". Simple is relative, of course, but if you're a developer, you'll likely find it simple, and it does fit your "deploy with a single command" requirement. https://pages.cloudflare.com/
You can also tie it with the free plan for Cloudflare Workers if you have some need beyond static pages.
For Github, yes. For anything else, you would have to use their rancher tool and Cloudflare KV store. I imagine they have plans to support other providers, but aren't quite there yet.
Seems like a great way to go, and if they implemented a Netlify CMS-like feature as well, that would really put it over the top as a unified one-stop shop for DNS/CDN/static site hosting + authoring built-in, and it also has Workers for any functions/dynamic pieces that might be needed.. all on Cloudflare's metal/edge. Sounds almost too good to be true..
Some people aren't fans of the built-in protection and feel it's a bit overzealous in throwing up catpchas to certain visitors. No CMS feature. I do like it quite a lot.
You can also tie it with the free plan for Cloudflare Workers if you have some need beyond static pages.