Simple.
No matter who you are, what you work at, how much you make, or what you do for a hobby, you are a human being.
You have flaws.
One of the flaws of a human being is blind rage, which we have all experienced at one point or another in our lives.
And sure, as you have stated yourself, the repercussions are usually much bigger than the instant gratification.
But the point is, sometimes you simply cannot control yourself, because it's easy to sit on the couch and say "well that was stupid, it's only a HBP", but what you need to understand here is the fact that a person can only take so much of a certain situation that's making him uncomfortable before snapping.
Even if you're a professional, even if you make millions of dollars, you're still human.
And unlike what you said earlier, rationale is not the only part of being human, so are emotions, and emotions sometimes cannot be controlled.
For the last time, ballplayers are not robots.