Very rapid learned behaviour combined with amplified selection. Boats = food sources. Sharks that follow boats get a feed, thrive, make more babies. EDIT: Combined with more pressure on food sources, you can see why sharks would opt for an easy feed. If prey biomass was at historic levels I bet there would be epic numbers of sharks but they would be happily snacking on random fish rather than looking for ones on a hook.
Probably an unpopular opinion but if a few more of them got killed when brought to the boat it would start to reverse the behaviour.
re. what Steps was saying about how we protect the top of the food chain but say stuff it to the beasties lower down, yep, documented phenomenon, it's called "charismatic megafauna" and it's basically that lots of people feel bad about harming a few big things but less bad about killing lots of small ones. Good example is people having a huge hardon for T&R of young, extremely fast growing, relatively prolific Striped Marlin but happily spiking a 40 year old Snapper and dropping it in the chilly bin.