F'real they're just better SUVs. I tried googling it, but the internet's very helpful answers were "they're not cool" and "SUVs are more popular." I'm convinced it's manufactured desire. What really happened to the minivan?
Edit: Apparently wagons and minivans still exist, they're just sold as SUVs.
I learned from a terrible person in my orbit that Good Morning America did a segment recently about how the minivan is making a comeback. My guess is that the absurd used car market right now has gotten through all the stuff people actually want and all that's left to buy is minivans.