Earlier quoted context omitted.
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 det…
In one case I offered to (and actually did) convert the Word docs they sent me to the appropriate Hugo markdown with front matter and push it for them (not a huge effort, maybe 10 mins per post, I was happy to do it). It worked for a bit but they still ended up pushing for a Wordpress site. So yeah, it's not down to technical experience required for the edit process.
Because they don't want to call you every time the need to fix a spelling mistake, or adjust fonts or colors or layout, or add/remove a section. What if you're busy or on vacation?
It may also be your personality - do you think you may come off as inflexible and arrogant to your colleagues?