They make choice, because they're the ones working with this daily. Their goal is to put content on display fast. Content varies a lot - often containing for eg. tables, which simply don't work well in markdown or images you need to host somewhere.

I spent a lot of time looking and still hasn't found toolchain, that would allow interns with zero technical experience deliver edits, without getting involved in tech details.

Closest one would be some headless CMS with Static site generator bolted on top, but honestly they all suck.