There was a time when vibrators and dildos had next to no detailing for added pleasure, and they were all pretty standard shaft shapes that came nowhere near reaching the possible pleasure plateaus of the pussies they are pounding.
Over time as the sexual revolution changed society so that women could get toys better suited for multii-orgasmic masturbation sessions like this one at FuckHerRight.com, the makers realized that just like any guy, to be effective you gotta have balls…in the case of ben-wa balls, you can have balls of steel.