in all honesty i don't think they're more of a money laundering scheme than any other business.
mattresses are one of the few things that people still want to feel and touch in person before they buy, so that is what is keeping physical locations open. depending on the size of the store they might only need 1 or 2 employees on the floor at a time, so it's not like they're paying 50 employees.
and they don't really lose their value, aint no 2024 model sealy dropping that makes all the other ones in stock lose half their value like that. it's kind of one of those can't reinvent the wheel type things.
and that just goes for strictly mattress stores, most places sell other furniture to go along with it.