That doesn't tally with statistics.
Gucci has grown by 12% in the last year on top of growth the previous, and continues to rise in market share. Meanwhile their largest age demographic has shifted 'down' from the 30-40 to 20-30. Miu Miu, Dior and Burberry have all made clear indications in the marketing and strategy to 'rejuvenate' to appeal this same younger demographic.
Don't forget. The market is now global, the US may have less growth but that's
growth not shrinkage of sales. If everyone bought the same last year as they did the year before that would be 0% growth. Brands are looking for us to spend more item per item, on more items or need to sell to more people
too.
Since there has been such huge growth in the past decade over less saturated markets geographically (Russia, S. America, China, Korea etc) that slowed down a few years ago, the only way to continue the rates of growth shareholders value and became used to, is to capture the imagination and money of those that traditionally bought middle-brand or are buying for the first time. Not only are these premium stores stocking more 'cute' stock but the actual stores themselves are redecorated to be less intimidating and imposing to young buyers and now look more like theme parks/sports stores.
In the early/mid-'90s the was much talk of
Gen X opting out of the capitalist/consumerist model of the former gen ('greedy' yuppies with their status bling/bags). Grunge, slackers and crusties were all supposed to shun shopping. Though I'm a bit younger I remember I carrying a Samsonite cabin bag all my student years. Since teaching, I've seen the Wangs and MbMJs (carried about like they were the crown jewels) come and go, now it's vintage and new Chanel and LV, they are mostly 18-21. This flies in the face of commentators reporting on Gen Y & Z supposedly seeking 'authenticity' through experience and shopping locally. We also know that holidays, theatre tickets, and gardening tools for allotments and small holdings are still products. Nothing is authentic because it's all just clever marketing and hype to make us buy more/different stuff.