The increasing frequency of shark attacks on humans is due to diminishing baitfish, in turn due to the growing world population.
Sharks have been congregating in large numbers around the Florida Peninsula for....who knows how long? I suspect it's more than food (or lack thereof) that attracts them to the shallows. There are enough protected waters near Florida where there is effectively no fishing. If it were strictly a matter of food, then the sharks would be found there in disproportionate numbers.