There is no reasonable expectation to help anyone, I.e. no law requiring you to help anyone.
There is a "Good Samaritan Law" that protects you from most things when rendering aid. There are both areas where these ideas are valid, people are usually willing to help, but most of the time they would rather steer clear until LEO or paramedics arrive. Being a boat crash, they may have felt the situation was dangerous, and shouldn't approach. I've helped a few people in the past few years, both medically and tows/mechanically.
I went to give someone some crickets after fishing a few years back, they had been fishing a spot for a while. Motored over to see if they wanted the crickets, and they were waiting for a tow. Had been waiting a hour for someone they knew to come get them. I hooked to them and towed them back to the house, no telling how long they would have set there.
That being said, Not everyone is comfortable with engaging other strangers, if I noticed a boat crash, I'd go make sure everything is ok, long as there are no flames. I usually keep a good first aid kit in my vehicles.
Fishing is a science, study, experiment, fail, and succeed...then start over tomorrow. Yeah I'm a science guy.
03 18ft Xpress Jon boat Center console 90 HP 4stroke Yamaha Humminbird 1199HD SI
97 14ft Polar Kraft Jon boat 85 Johnson 30hp Lowrance Elite 5 DSI