Millenials are post-modernist, their fashion and general attitude is baked in facade. Hipster fashion for example was a pastiche of 20th century working class wear, which is why they featured leather jackets, sun hats or dock-worker beanies, aviator shades and weird boots but all produced and procured by non-working class fasion designers
Gen Z are Post-Postmodernism (New Sincerity et al) and their fashion is more about personal comfort than pastiche, so they have wide flowing pants and crop tops