I think you do it because that is how the body and brain react. Humans are problem solvers. Show us a problem, and we react. Sometimes we solve them one at a time and miss the big picture. There is less choice in the matter sometimes than we would like in hindsight. Maybe that boat was going down whether anyone tried to save it. Maybe it could be saved. This time it was saved.
You yell, "duck!" and it is the one who rationalizes, "which species?" who gets clocked with the boom!
I bet more of us would be on that boat instantly trying to save it than not. I know I would.
Humans also have a survival instinct. Our internal alarm that says, "get off! Now!" so we do.
I was 5 years old when my father took us to Riviera Beach, Florida. Odd that Floridians who live on the beach went to another beach, but I digress. When we got to the beach, a barge was aground and had been rusting away. People were climbing on it and enjoying the spray of waves that were breaking on it broadside. My dad took all of us children onto the slanted deck. My 3 sisters and my dad's girlfriend climbed about halfway up. My dad, brother, and I climbed to the highside of the rusty hulk. I felt uneasy up there. Anyway, I spotted a wave coming that triggered me to run down the deck and right onto the beach. That wave triggered my survival instinct. The wave hit, washed over the railing, and swept the girlfriend and sisters down onto the deck where they suffered lacerations to their thighs and buttocks. They spent the night in the hospital getting treated.
They did not see the wave. I did.
MainSail would have gotten off that yacht. Trust him for that.