Also, any "deep dish" floor mats are more expensive to ship as they are not flat.
My P2 (Platform #2 2001-2007) Volvo V70/S60/S80 has a deeper footwell and none of the mat makers make one.
My footwell is so deep I'd fear buckling at the corners with any "universal fit" mat.
In the case of my Volvo, there weren't that many sold in the No. American market so it is a prime candidate of a vehicle to be left off the catalog.
Also: As mentioned above, a "walking" floor mat can easily cause crashes.