This may seem snarky, but I think corporate marketing departments cause trend. I'm sure it's easier for companies to make various riffs on a single scent theme, than to continually invest energy in creating the new.
If a company can convince consumers that virtually identical scents that follow the same formula are cutting edge and hip, and people buy them without concern for uniqueness, why wouldn't they actively reinforce trends?
I don't think it's coincidence that perfume trends have solidified as business strategies like market targeting and segmentation, cost-cutting through economies of scale, etc. (all aiming toward efficiency and easy profit) have become more sophisticated and purposeful.