Most don't, they typically are looking for a specific range of prey or food items which don't include humans.

One caveat is a personal observation and anecdote of mine, I grew up surf fishing west of Galveston and within the first few sandbars where the vast majority of people are swimming the average size for any species is sub 3 foot, and usually way smaller. In years of surffishing I've probably caught 4-5 with enough size to dress out and deep fry- which, still was just the thickest portion of the tail. Swimming back in while reeling and fighting them usually did them in

And the 3-5 footers I've seen on the beach where usually brought in by kayakers fishing out past the breakers and the swimmers.

That included blacktips hammerheads, and bonnetheads mostly, and when there is an incident it's usually a fairly small shark which GTFO's after an exploratory nip.

So my theory is the main few that are ok with some manslaughter- bulls, hammerheads, whites etc. still exercise selection and there is very little intersection between the shark with the size and confidence to eat you and your availability to be eaten.

One little known factoid is possibly the single most willing and capable predators of man is not a tiger or polar bear, but the Oceanic whitetip, which is strictly blue water and may show up en mass on site of maritime disasters with no hesitation to start a feeding frenzy and literally kill, maim and eat as many people as are stuck in the water, tens, hundreds or even thousands.