Fashion dictates what latest style one should wear.  This is decided by people who work for the companies that want to sell you their products, and to maximise their profit, fashion has to change frequently they they can maximise their sales.   Huge budgets for marketing and PR are used to convince you to buy the products they want you to by.  Those who resist their push to increase consumption, and un-fashionable and "out" - what a terrible state to be in!   You need new clothes all the time, and durability in clothes is discouraged.   Celebrities and marketers/influencers are used to manipulate the ones who need to copy what is currently fashionable. 

Fashion is mostly made by large corporations, who aim at profit for their owners/shareholders in the next financial years.