I think it's as simple as that, but I would change it to "if your football team has been good for a generation, then people like it."
I'm almost 50. I grew up with the Vikings going to Super Bowls and the Gophers being mediocre to bad. It's not very hard to figure out why this is an NFL town. The Vikings have been mostly mediocre since the 80s, but the've popped up and gone to NFC championship games once a decade, just enoug to keep fans in the fold. Now, my friends want the Gophers to win, sure, but their football commitment is focused on Sunday. When I bring a friend to a Gopheor game, they have a good time ... but they're not ready to go all in.
I do think there's another generational issue: people got used to the comfort of the dome. I'm with those who believe that if the weather was the same this weekend as last, the stadium would be full. I'll be interested to see what happens for Viking games at the end of December.