Who Changes the Kissing Rules?

A female friend who I hadn’t seen in several months and I greeted each other yesterday with the usual hug and one-cheek kiss. If I had done this in 1970 I would have been looked on as really weird, or I might even have been slapped.
The social norm on kissing has changed in the U.S.; and the norm elsewhere is different: In much of Europe the two-cheek greeting between friends of the opposite sex is standard.
On my first return trip to the Netherlands, I assumed that two-cheek kissing was the norm there. That nearly cost me a broken nose, as the norm there is now the three-cheek greeting kiss. My Dutch friend tells me that the norm changed in the 1980’s or so.
Why do norms change? Does some highly visible individual start the new custom? Do we adopt it from elsewhere (which can’t explain the Dutch three-cheek kiss), so that we Americans might soon be doing an Arab or Latin male-to-male hug/kiss? Given the importance of social norms in conditioning market transactions, it would be good to know where these norms come from and why they change.