maybe they can't use magic attacks due to lore reasons....
Yeah some people just miss core class features, to me a ninja not using mudras is pretty much the same complaint as healers not using damage (which i see so often) or a tank not using mitigations.

I think when I was a sprout my first dungeon (the first ARR one) i was confused what my tank stance did i kept spamming it off and on like a random cooldown, I think i thought it increased healing or something? I was very confused to say the least. I did provoke the bosses at least...

Somepeople are learning which is fine, I'd find it concerning if a ninja wasn't using murda's at 90 dungeons or later ones though. Although i don't think id say anything just incase because y'know its ff14 lol.