Those asses are grotesque.
The common excuse is "OMG, ur dick can't fit!" but of course, that argument is shit considering the many other positions you can have with a woman with such a large derriere. Not to mention that your dick can still get in there from the back but it is still a grotesque mass that will explode to something horrific 5-10 years down the road when her metabolism drops and she waddles around, making it impossible for anyone else to get past her in an aisle.