I'm not sure this is true. I buy used stuff all the time, even though I can afford new stuff. All my clothes are second-hand.
The reason I do that is because I can ascertain the quality of the clothing and determine that, despite them being cheaper and used, they are just as good if not better.
I'm sure there's a lot of parents who assume, incorrectly, that a used and relatively clean car seat is just as good as a new one. So, they save a few bucks because why not?