Especially for athletic gear, the ones with huge branding is cheaper when considering quality you get and how long it will last.
But I've dropped $50+ each on plain tshirts multiple times too. I've got some that are probably a decade old and some that are less than six months old but no idea which are which because that's how well they hold up.
I've also got a bunch of cheap ones for stuff like yardwork.
But for people that buy heavily branded sports clothing for it's intended purpose, the heavy branding actually makes it cheaper than competitors and everyone is aware of it.
The thing is those people tend to be in good shape and will wear that stuff out and about in town. And anything attractive people wear, is what everyone will start buying.
Like, yoga pants started being worn as regular pants by women who actually did yoga. They tended to have nice buts from yoga, so then other women just started wearing them expecting the same thing.
Or like how Carhartt made an entire new line of clothes that is nowhere near as rugged yet more expensive, just because people want the "rough" look.
It's just people who are emulating others without understanding what they're emulating, that's why teenagers and 20 somethings are always the hardest hit by this stuff.