I don't think these companies want the poor people to wear their brand.

They'll find another way to destroy them.

2018 article reports that Burberry destroyed £28 millions worth of clothes to keep their brand "exclusive": https://www.bbc.com/news/business-44885983

The intended effect of the law is that they get better at planning. It requires supply chain innovation similar to what happened in the automotive industry decades ago with JIT manufacturing. They can borrow from fast-fashion but now there’s a penalty for over producing.