They seem to follow the trend of the short/mini yukata. Why it's also that short for men when that has never been the style for men, I have no idea lol.

I think so far the only armor I've seen with animated sleeves is the Divine Harvest/Divine Death robes. It's possible the new yukatas were made before sleeve movement was tested (almost as if right now they're testing sleeves with movement with those 2 robes) or they just didn't want to bother since the original yukatas from 1.X probably didn't have moving sleeves.