Not a true statement. Roughly 35% of any given wardroom on a sub is non-stem, with no impact to career progression.
There's also no data regarding whether tech majors attrite from the pipeline at a different rate than non tech majors. Getting a B+ or better in the pre-requisite courses and having good SAT scores seems to sufficiently predict success.
Of note, the S in STEM doesn't count as technical as far as the nuke community is concerned, so something like a chemistry degree might as well be a BA in theater.