For many women, dude being bisexual equals dude being gay, PERIOD
For them, once gay, always gay.
Doesn't matter how many girls the dude has bagged or is currently bagging, they would never date him any sooner than they would date any of their gay friends.
I don't think it's prejudice, it's simply drawing a line (of them not wanting to be with a guy who has been with another guy).
Call it old fashioned or prude, it is what it is.
Sure the episode here shows the bisexuals in a pretty bad exaggerated light, but you do have to accept the prominent ones do often give a bad name to the real ones (almost all the famous bisexual women when marrying do end up married to guys, and so do the bisexual guys).