Some people do it for the money, some people do it because they are uneducated...
People seem to get the impression that by overpowering a horse by riding it as a yearling, they have somehow mastered the art of breaking. Yearlings are so small and unbalanced, they hardly put up a fight, and are too dumb to know what's really going on.
It's just people who are too coward to teach their horse anything and think they need to overpower it to train it. I have the same beef with people who "tie-train" month-old babies. It's not training, it's just because they wear out faster and give up.
It's a dangerous way of thinking, because you'll always have to "up" yourself to overpower your horse, bigger spurs, bigger bits, bigger chains.
But the fact is, a human cannot overpower a horse kindly. I prefer humans use their superior "brains" to be educators, not masters.