While the mechanics of social change remain pretty mysterious, one of the underlying elements is "what is normal" -- people want, generally, to be normal, to be, to think, to behave in the ways that "normal" people, or "average" people in their society do.
Take one small instance of a behavior that is relevant here. Consider an attractive woman who works in a retail or retail-like context frequented by men. Perhaps she sells shirts. Perhaps she's the marketing director at a high tech firm, who staffs the booth at the trade shows. Invariably this woman will be able to tell you endless stories of men who felt it appropriate to touch her. Usually something benign like placing his hand on her shoulder or in the small of her back.
These men are doing this, mostly, because they want to touch her. They know they can get away with it because she wants to keep her job and sell them a shirt, so she's unlikely to create an awkward scene by requesting that the hand please leave even, though, as a general rule, she would prefer to not be touched. You can argue that it's her fault for taking a job selling shirts, but a) your argument, whatever it is, is silly and b) that's a different discussion.
This is not "frequent", this is not "common", this is universal.
Ok, so, how does this change? It changes when men, as a general rule, feel that such behavior is "icky" or "just not done" or "simply not cricket" or whatever. They still want to touch the pretty girl, but they don't, because it's abnormal, it's what weirdos do and the one thing they're sure of is that they're not weirdos. Or at any rate they don't want anyone to think they are.
How does THAT change? That perception of what "normal" is?
That's a bit mysterious, but people acting out on the street probably has a non-zero impact.
Interestingly, photography and art play a role. If people are constantly touching shopgirls in movies, in adverts, in magazines, in books, then the standard for "normal" is arguably that touching shopgirls is fine. Do photography and art merely reflect the current zeitgeist? Are they merely a record of what is currently "normal"? Or do they actually affect the social consensus? I think it's a bit of both, but you can certainly find arguments on either side of that.