Why would I want my WIP site to be on the public internet? This has been built into Jekyll for years. Probably other SSGs too but I don't know/use them.
Because you're thinking in the context of a solo developer working on their site locally. You don't need a CMS. People that want to collaboratively work on a website, some of which may lack technical skills, need a way of previewing their edits that doesn't involve running shell commands.
You're conflating the two unnecessarily. There's no reason Jekyll's server has to run on the editor's local machine. See my other comment about jekyll-admin which can be used collaboratively: https://news.ycombinator.com/item?id=47737324
I don't see much of a difference between `jekyll serve` and the e.g. `service nginx start && service php-fpm start && service mariadb start` that would be needed to run WordPress. In fact I don't run my WIP Jekyll site on the same machine that I edit from. Mine is available only on my personal mesh VPN, but it could easily be available publicly if I wanted it to be.
