America is huge and you might have to drive very far to get that second hand item. Also not everyone has a pickup truck to go get bulky heavy furniture you can't take apart to easily transport to your place. And bedbugs are an issue in some places, especially major cities. It's possible for some but not everyone.

I mean facebook marketplace and craigslist you're just as likely to find furniture that's already from IKEA or some similar retailer, anything better will likely cost way more unless someone really wants to get rid of it.

Also it should be no surprise that used IKEA furniture will also be way cheaper.