There's actually a not so recent
song by a German comedy band on the topic of shaving one's pubes as a male. It's in German, unfortunately, but it's funny still.
I can't talk about women but gay men differ on that topic, too. I guess it's kind of a trend. During the metrosexual phase everything had to shaved and not a hair should be seen. I don't know if something came in between but the next thing I remember is lumbersexual with the hairy, burly man as a central part. So "wearing hair" was in again. Some are still stuck in the metrosexual phase when it comes to shaving or just don't want have "a jungle while giving head" (someone said that to me).
But cekay82 is right too, I guess, many think it's expected, especially when you're seen by a bigger crowd (or in this case audience).
I think it also comes from the influence of the porn industry. Most professional porn actors I've seen are shaved. So maybe that's model?