The vendors are just too lazy to update their listings for the new model year.
I just reached out about one for sale on ebay (link below) and asked why it fits the 2020, but not the 2021 and their only reply was "Sorry, it doesn't fit a 2021."
So not sure if it is lazy vs uninformed. But I'm not chancing it. Looks like I'll have to spend a a grand to piece together a MOPAR rear steel bumper.