Just a word of clarification;
Top fuel hydroplanes love the canopy. But for other reasons. If you do not have them, you are not allowed seat belts of any kind. Who wants to fly across the water at 240 mph? The force of the water is a main cause of injury. Pavement cannot flow inside the roll cage freely at speed, but water can. The canopies almost eliminate this. And another quick fact is that the capsules are in no way water tight. Not even close. I have one in my garage. Come on over some time and check it out.
And lastly, the canopies keep you in the boat and almost eliminate injuries from the boat coming back to hit you. That is where many people get hurt.