I was just reading "Instant Replay" again (Jerry Kramer's NFL diary from the season leading up the Ice Bowl/SBII, if you've not read it); he describes how the Packers were expected to be nice, never to fire back, never to get into the verbal exchange game...and how it drove him nuts. He could get worked up into a pretty good lather by game time, which I imagine was at least part of Lombardi's intent.
I read that book about a zillion times when I was younger. Lombardi tried to get his team to act like the consummate professionals. He was frustrated too with the antics of Hornung and McGee. He wanted his team to have a winner's attitude about them that made it seem like winning was just another day at the office. In his opinion they didn't need to talk big. They just needed to show up and win.
But there is another factor in today's league. One I don't appreciate, but it's there nonetheless. Partly because of fantasy football and a number of other factors, this has become a player-centric league rather than a team-centric league. So guys tend to do things to draw attention to themselves. They gain free publicity and presumably sell more products for themselves. Even things like Finley's touchdown celebration isn't a "TO" imitation. It is an self promoting advertisement.