There have been many threads comparing shark attacks to other stuff, most of which I find pointless. I believe I have a "rational fear", and not from watching Jaws in 1975. I've known sharks can kill you since I was a little kid. I also know that planes can crash and think of that every time I board one. Yet I doubt anyone has less of a fear of flying than me. But just as I don't seek out sharks, if I had unlimited money I wouldn't fly unless I had to go somewhere.
Fear of an animal that is vanishingly unlikely to attack you (shark) is not a rational fear, just as fear of the safest means of travel (commercial airplane) is not a rational fear. And allowing such fears to rule your life is not a rational choice.
I am very afraid of flying. But knowing that the fear is irrational, I don't allow it to prevent me from traveling. Coming face-on with a shark (which has only happened to me on a shark dive; otherwise they're always swimming away) is very scary, but knowing they are less likely to harm me than that doofus talking on his cell phone while driving next to me on the freeway, I can enjoy their impressive beauty.
Yes, sharks can kill you. They have lots of big, sharp, scary teeth. But you live every day with things that can kill you and are much more likely to, such as your car.
But as to why more people don't take up scuba diving, I think it's largely the rational fear of being so far from open air. Also, of course, being unable to swim (a very good reason for not diving, if you can't swim.) I have a friend who loves to snorkel, but is terrified of the idea of being in water too deep to see the bottom. I was scared of the idea of having to take my mask off under water, and fearful that I'd get water up my nose when I did so. (Until someone suggested taking my mask off at the surface while snorkeling, where it would be easy to life my head above water. I discovered to my surprise that I could breathe through my mouth and not get water up my nose. But it was still difficult to take my mask off under water, and I managed it only because a very patient instructor took me though it by baby steps.) We are land animals and below the surface of the water is very foreign to us.
And there are indeed dangers down there. Sharks are not particularly dangerous if respected, but there are poisonous critters and critters much more aggressive than sharks, and equipment can fail, or you can get bad air, and any medical emergency is much more critical 60 or 100 feet down.
And sadly, most people are indeed governed by their irrational fears while at the same time engaging in activities that are truly dangerous without even thinking of the danger.
And finally, no sport appeals to everyone. Plenty of people are just not attracted to the joys we experience while diving, or they prefer to spend their disposable income in other ways.