My guess: fast fashion came with very cheap prices per item, keeping overall spending stable or rising through increased consumption. Now the novelty of ridiculously short wardrobe replacement intervals is starting to wear off, but the prices are here to stay.

Expect retail area dedicated to cheap (formerly known as fast) fashion to shrink accordingly. Probably not a big loss if the continuous network of direct sightlines between H&M stores is getting a few gaps here and there.