How do trends and fashion work in all areas (clothing, entertainment, technology, fandom, etc.)?

I mean the psychological and social mechanisms.

Especially concerning trends/hypes which are obviously created to 'cash in' and have obvious drawbacks for some of the stakeholders? (For example, how is it possible, that 'youtube influencers' 'work', it is clear they want to make money/sell stuff and still they get an audience. Why?)

Book recommendations to learn about the psychological/social basics regarding this question/topic also highly appreciated.