An Americas cup challenge boat. There's a rib never more than a couple of hundred feet away and probably a chopper too. The weather in this video is probably the heaviest they leave the dock in and they rarely get more than 10 miles from home base. Lifejackets would only fit about 1/2 the gorillas on board and would restrict their movements even if they did.
Lifejackets ....... They'd get laughed off the water!