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.
