Sorry for such a long delayed reply.
Part of the reason is that quality has come down in the last 10 years or so.
Example: balenciaga jackets and McQueen jackets used to have silk or silk blend linings. Now they are mostly polyester.
I also see
Prada charge 3k for viscose dresses which just looks wrong.
I for one have an issue buying synthetic items from designers. On the other hand, plenty of options on the resale market with much better quality and fabric. So why not?
All these will lead to the demise of department stores imho.