I'm gonna say that I haven't seen my friends nude because I'm not including "friends" who I have slept with at one point.....
As far as strictly platonic friends goes, I think I've been socialized to think it's just weird to see them nude. I'd rather not, and just have everything left up to imagination. Even with dudes I'm interested in romantically. Yes, I'm visually stimulated like any other red-blooded male and if we're dating, I do wanna see you naked at some point. But I like to get to know you first. I don't even want to receive dick and ass pics. Maybe I'm just a prude.