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?
The odds for favorites are low, but chances to win is high. But despite this, many of us prefer to take the safe side even with small profit. If you bet often on favorites, consistent winning is possible, it's not boring but more on it's not exciting.
I tried to bet on underdogs too, though the profit is way better, there's a slim chance to win. Thus i'd rather win consistently with favorites than take risk to underdogs. Winning is the goal here btw.