I do use Jekyll, but given that a site will live for a few years at least, babysitting a ruby app isn't something I look forward to. Maybe my server has a different ruby version from my desktop, maybe some ruby gems are installed by my distribution and some others I have to install manually via gem leading to an inconsistent system state, every now and then something breaks, some functionality is provided by a gem I have to install manually and oops, I forgot to ssh to my server and install it there too. Oh, some gems can't be build because my server is hardened. Maybe jekyll got a new version and this leads to new ruby adventures.
Hugo has some other niceties too, like a built-in server with live reload and some clever link translating while testing on localhost.