North Americans, in general, have a hard time with sports that require continuous attention.
Baseball and Runball are brutally stop and go which means it's easy to know when to pay attention. Hockey and basketball less so but there is still quite a bit of down time.
Football requires people to pay attention all the time. Doesn't translate well for audiences with short attention spans who need to be told when to pay attention.
Could be, I'll give you a bit of a different take. I've never been a big soccer fan, never played it and didn't really understand it. The only time I would watch was the World Cup and only passively since the 80s. But this year I've watched no less than 20 games and probably more, it's been fantastic. Yeah, I don't really like the rolling around but the skill on these guys is incredible, wow. I've really enjoyed it and am sure I will arrange my schedule to watch pretty much every remaining game. Obviously I've gotten to understand it much better with so much viewing, I haven't picked a favourite team yet but probably will this week.
As an aside, I lived in Little Italy Toronto during 1982 when they won. People began spilling onto the streets and were firing guns into the air, it was nuts. I figured I'd better get out of there or I would have been land-locked for days, I had to drive on sidewalks to get out.