In sports, there is always someone winning dominantly. It can get to a point where they are almost always expected to win. By that point do you continue to bet on those favorites to keep winning or does it bore you? Would you enjoy stirring it up a bit just for the fun of it and betting on the underdogs even if the chances are quite low?
Personally, and honestly, I usually bet on sports by betting on my favorite team. It's not boring as long as it's entertaining to watch the game, and it's usually characterized by dominance and lots of action from that favorite team. I often do this in soccer matches. However, that doesn't mean I never choose to bet on the underdog. I remember I've tried betting on such matches, but I was just experimenting. Usually, it was because I believed in a player (or several players, if I could trust them) who might influence their game, or perhaps a new coach implementing a new strategy. So I tried my luck while enjoying the game.