Because they make ridiculous amounts of money. There are very few people who can do the job, it's extremely dangerous and even if you don't get injured or killed, it's very hard on your body. Iirc most divers only do it 2-3 times a year because it takes a long time to safely decompress at the depths they usually work at (it can take days or even weeks) and then they have to take time off to physically and mentally recover.