I don't think it's difficult, but there aren't the same number of people that know Wordpress. For content editors, I don't think it matters - but for programmers, I can find people that know Wordpress. Finding someone that knows a given static site generator is much harder.
Any good static site generator can be learned in an hour.
You shouldn't search only for people who already know the static site generator you plan to use: any good developer that uses the CLI will have no problem using it.
