I think it would be interesting to do a poll asking people to rank the four major sports in terms of their level of interest. Then you could ask why they chose that rank. I read somewhere Americans like higher scoring sports like basketball and football than lower scoring sports. Maybe hockey is boring to some people like tennis is to most people.
I think if the NHL advertises the sport hard enough it will expand. Maybe someday the league moves into Mexico and truly becomes a North American league.