> IMO many software developers are just not fast enough at writing or language
I think this is the overwhelming factor, software engineering doesn't select for communication skills (and plenty of SEs will mock that as a field of study), or at least most SEs don't start out with them.
> SEs will mock that as a field of study
Who are these people? I've never encountered that. In my experience engineers who aren't great at communication freely own up to it.