Well, you can buy new clothing that isn't "fast fashion".
I rarely do though. For something special that I'll wear forever, yes. The rest of the time it's eBay (which I've been using since 2004!), Vinted, sometimes Etsy or other second-hand platforms. Also charity shops & vintage shops & markets - but more so for jewellery, bags, sunglasses etc that don't depend on me being a size 10 anymore!!
Originally it was to shop for vintage.
Then I started to set up searches for things that had sold out/expensive items that I didn't want to spend full price on.
Then sustainability became a large part of the reasoning.
And now it's also because I'm no longer quite well-to-do, & am instead a poor freelancer who can't afford to buy new!
I genuinely don't feel constrained by that - the thrill of the chase has always been a real pleasure & I still find it so much fun. And I do feel good that it's better for the environment.