I must have missed the part of my own comment where I suggested that the strange part of this was that those people were allowed onto a boat.

The strange part is that they wanted to be there. If you can't swim, this is a self-evidently bad idea. People are still afraid of boats, just as people are afraid of airplanes. Those people are correct -- occupying a vehicle whose failure will instantly kill you is something you should be frightened of.

But since you mention requirements, I'll note that my parents would not allow me on a boat -- any boat -- before I could swim. Unlike the ability to fly, the ability to swim is not all that difficult to learn. And while it won't save you if you get dumped into the middle of the sea, it will save you if you get dumped twenty feet from shore.