Ahhhh found that interview I was looking for! Here, Fassbender states it pretty well :
"You’re in a position where people treat you differently. Maybe a lot of people are in denial and think that it’s down to their looks and their charm that a lot of women proposition them, but the fact of that matter is they are living with what appears to be an attractive lifestyle. Your opportunities are multiplied again, so there’s more of a buffet of choice.”
Dead on. It all has to do with privilege and dare I say power. Some people are attracted by the lifestyle and want a glimpse of it, the whole "I slept with a celeb" and not because they are in fact attracted by the guy; further more, besides it some women love power and wealth, hence why you'd see some women going for ugly millionaires/billionaires and most importantly influential men, it may sound cliché but it is true, influence and wealth are the most powerful combination. Do you think the Marchesa girl would have looked at Harvey Weinstein if he was just an actor? Nope. She loves power. And look where it got her : Uncle Harvey is shoving down people's throat the Marchesa dresses on the red carpet, which most of the time are really fug imo. Do you think if Jay Z was just another rapper, Beyoncé would have gone for him? I tend to doubt so. Power, privilege, influence.
Now like I said, Fassbender is mostly seen as a sexual fantasy by women so he belongs to the "I slept with a celeb" category imo. Pretty sure if Fassbender were a regular Joe, I mean yes he'd still get laid, but he wouldn't have all the pretties throwing themselves at him, he'd be more like "that guy from the club"... aaaand he'd be my party mate
I believe it all depends on the people's nature and new found privilege you get and how much it may get to your head. Now I really can't speak for anyone/everyone on that matter, but I know that not everyone is attracted to that lifestyle or want to go for a famous person etc.
Funny thing is, working in PR/media I see things differently; many celebs I've met and oh my god I know I so wouldn't but some co-workers go for it. BUT if I were famous I so would... an ego/power thing you name it.