People have loved watching sporting events for many centuries, and television certainly didn't popularize sports. But there's no question that TV changed the way that people watched sports, and sports on TV offer some viewing opportunities that watching sports in person can't match.
Some sports work especially well on TV because their scale or pace can make them difficult to follow in person. When spectators watch auto racing on TV, it's much easier to keep track of particular drivers and the overall state of the race, and the complexity of American football is much easier to sort out with benefit of multiple camera angles and announcers' commentary.
Other sports fare well on TV because the spectacle and pageantry of televised events is a good match for the traditional drama of the sport. High-profile boxing matches and mixed martial arts events are tailor-made for the hype of television, and pay-per-view events duplicate the special-occasion feeling of going to see the big fight in a glitzy arena.
Sports also benefit from the analysis, dissection and editorializing of experts, both during event broadcasts and on stand-alone sports news and commentary programs. Sports analysis programming is so popular, in fact, that entire networks, from ESPN to Fox Sports, have been created to support the genre.