Well TMP takes place in 2273 IIRC and TWOK takes place in 2285/86. Uniform trends and stuff can change with in that big gap of time.
Again, it's not just a fashion trend, it's a complete change in philosophy. Enlisted personnel were considered worthy of officer-style uniforms, and then they weren't. That's a drastic -- and many would say retrograde --change in recognition of their status.