I was also basing it on the fact that space travel is a lot more common in Star Trek's time than it is today. It really is analogous to modern day sea travel. Unlike NASA, you have people going into space just to do "menial" or "routine" stuff like serving food, cleaning, or whatever. Now yes, there are likely cases of people doing these jobs doubling up and contributing to the "more important" tasks, particularly on smaller ships just like happens today, but in the end, not everyone in Starfleet is going to have the equivalent of a few PHDs, or even be Academy graduates or even have any post-secondary education. Hell, there is canonical precedent in on screen material for this notion, given Simon Tarses in The Drumhead even said he chose to go the enlisted route as opposed to becoming an officer exactly because he was 18 and not interested in spending years in a classroom.
