There is a clear "cut-off" point for a dildo. It can incorporate the balls, or not, but there's not much remaining options there. A disembodied penis is complete.
However, with a Fleshlight/pussy, there's a bit of an "ew" factor. Where is the outer edge of a pussy? How much flesh comes along, and what do you do with the edge? For example, follow these links (I'm not NSFWing the thread yet)
http://www.adultnoveltyworld.com/Cli...5562-06-bx.jpg
Cassia Riley Pussy Stroker
Somehow, it seems to step away from "sexy" and become more "psycho killer chopping up body parts".