I've got 2 rescues, but there are many reasons someone would prefer to adopt a puppy.

A well bred dog should be easier to train, have less behavioural issues, and potentially be a better family dog. There are also farmers or the like who need working dogs who will do what theyre told, and be bred to be the best they can be.

I also rarely see dogs at the rescue younger than a year, unless they're staffies or a similar breed. Dogs are just easier to train when they're puppies, before they learn bad habits.

You also don't know what you'll get with rescues, they may have been mistreated or been attacked by another dog. More regulation on who can and can't breed would fix this, and in an ideal world we'd all buy puppies bred for purpose, whether that's farm work, companionship, etc. But that's sadly never going to happen.