A key difference is the fanbase as well. Football is getting more and more americanized, consuming everything else but the sport itself. Additionally with this new stadium (similar to other new stadiums), a larger group of people visiting has no connection to the club. It is more of a tourist attraction than a place where it is going to be tough for the away team. And it doesnt help with away fans being more vocal in general.
One thing that has been the case is that people seem to be happy enough making a whole load of noise at the bars but by the time they get on the concourse they don’t wanna do it. Maybe we are just too self-conscious nowadays?