Because when men are raped, society treats it like it's a joke. They set it up in a place where it's a "ridiculous concept" but yet still push the idea that being raped is due to one's failure to assert his masculinity. Because of course, strong real men could never get raped

The effects are bound to be more damaging because whereas with females, people are more inclined to the "Guilty First, Innocent Later" approach, male rape is basically laughed off and ridiculed by the GP.

Also, I very much doubt it matters whether one is raped by a women or a man. Rape is rape - but female-on-male rape victims may be less inclined to report it as they may frame it as an enjoyable experience nevertheless.