Motorcycle Racing is sport
Racing is a sport, just like football, soccer, the Olympic Games, or a pie-eating contest. For the competitors that means it is a contest to see who is the best, the luckiest, and the most clever.
Racing as Entertainment
For the spectators, racing is entertainment no different than TV and no less varied in genres and styles. Sometimes it is about a quick thrill or a vicarious adrenaline rush. Sometimes it is about watching a master do something at a skill level you can hardly imagine.
Sometimes it is about watching drama and strategy play out over the course of a season. And sometimes it is just about big, dumb fun. If you find yourself not caring about racing, chances are you are watching (or participating in) the wrong type.
If you don't like one variety, try a different one. If you are one of those riders who see motorcycle riding as more of a zen thing, like surfing... well, they have surfing competitions, too.
All those are just some of the more popular, more common forms of motorcycle racing. Trying to explain why someone should care or appreciate motorcycle racing is like trying to answer the question, "What's so good about TV?" or "Why do you like sandwiches?"
