The way to think of sports, I think, is like fashion (I'm sure this isn't original to me). The rising and falling interest in sports over time is just a matter of changing tastes, rather than one sport or another being better or worse than another. Having just read Jeremy Schapp's "Cinderella Man" I was stunned to learn how popular boxing was in the 1930s compared to all other sports. Babe Ruth's scandalously large contracts during that era were a small fraction of the amount that Jack Dempsey would pull down for one fight. Today, boxing is a borderline fringe sport. Ditto for horse racing. The Olympics may or may not be in a permanent death spiral--I suspect that it is too early to tell. Hockey has gone from one of the country's "four major sports" to essentially the same level as Major League Soccer, and I think the NHL strike just expedited a trend that was already underway. It is now standard to refer to the "three major sports" in the U.S. Casual sports fans used to be expected and able to watch and politely talk about the Stanley Cup playoffs; today that is no longer the case.Zywicki's observation about the malleable trendiness of certain sports is well worth noting. When I first started following sports some thirty years ago, the sports landscape we know of today was much different than it was then. Baseball was inarguably the national pastime, with pro football battling with college football for second. The NBA was a distant third, with half-filled arenas and title games broadcast at 11:30 p.m., and college basketball a sideshow, with attention paid only when the "UCLA Invitational" reached the finals. Pro hockey had no Sun Belt presence worth noting, and soccer barely existed. And every four years, everyone watched the Olympics, and unless you were willing to plunk down cash to see closed circuit broadcasts of the event, no one saw the World Cup.
So, the World Cup is becoming more popular because, well, it is becoming more popular. For whatever reason, one can speculate. But I'm guessing it has little to do with the intrinsic merits of soccer and more to do with the fact that it is becoming part of the lexicon of the casual sports fan, perhaps because it is fun to be wrapped up in an event of such global proportions. But, for instance, I don't expect much crossover from the World Cup's popularity to MLS. In the sense I am thinking of it, MLS is essentially a different sport from the World Cup because it is wrapped in a different social network, not because it is somehow a different sport.
With individual sports, the landscape was even more different. When one spoke of tennis, it was almost exclusively of the men's game, and it was considered a major sport, light years ahead of golf in terms of popularity. Women's tennis was considered a novelty; some interest would be paid if Billie Jean King was in the finals, but beyond that, nothing. Not only would Muhammed Ali routinely defend his title on live prime time network TV, so too would fighters in lower weight classifications, like Carlos Monzon and Roberto Duran. Track and field was also a major sport in the U.S.; the annual dual meet between the US and Soviet Union was one of the big events of the late summer. The Indy 500 was much, much bigger than the Daytona 500; NASCAR was considered minor league, and A.J. Foyt and Mario Andretti routinely dominated that circuit when they deigned to race in it. The Triple Crown in horse racing was huge; you weren't a sports fan if you could not name the previous year's winners. And obviously, thirty years ago there was no cable sports TV to speak of; a fan pretty much got to see his local teams, the Game of the Week, and little else.
None of the changes over the last thirty years occurred overnight. In the U.S., cable television has pretty much obliterated the sports world we knew of back in 1975. It not only fueled the explosive growth of sports like football (both pro and college), where the public appetite can now be sated by wall-to-wall broadcasts of games over fall weekends, but it has also enabled other sports, like soccer and hockey, to survive even with a fraction of the public interest. It has created public interest in activities (X-Games, poker, hot dog eating, spelling bees) that weren't even imaginable as spectator sports thirty years ago, and given female athletes celebrity that exceed that of men in the same sport (as with tennis or U.S. soccer), at the same time that few people know who the heavyweight champion(s) is, or can name another male tennis player besides Roger Federer.
The changes fueled by cable television are what makes a broadcast of the World Cup possible in the U.S. Otherwise, it would be impossible to justify televising all sixty-four games of a tournament for a sport few English-speaking people in the country follow. With so many channels available, each of them appealing to a separate niche, televising Serbia v. Ivory Coast or Angola v. Iran becomes viable; American soccer viewers are now plentiful enough to sustain the needs of advertisers, so that even the lowest-rated games in the World Cup are higher than what would typically be shown by ESPN at that time.