Better control and domain ownership. Especially since setting up a static site is super easy with Netlify. Set up a repo in either GitHub and Gitlab and Netlify will take care of the rest. The biggest downside is that it's hard to get exposure. However, it works for me since my site is just a portfolio site.
Yes, netlify makes an open source CMS (single page app) which works with a bunch of static site generators. You can upload an image, edit the posts, and then the SPA will use github API to upload or edit.