"But, alas... no one has really answered my question yet. Why to Jamaicans think that tourists (Americans, Canadians, Germans, or wherever) always need something when we're on their beach? "

I'll answer it. Because the tourists have MORE than the Jamaican vendors too. Pure and simple, its about the cash. From their eyes, they see you in their country (which means you had to spend money to get there), staying at a hotel (which means you have money to spend to stay at the hotel) so you MUST have nuff money to spend a likkle with them.

You could go the AI route - that would be one solution (many AI properties allow certain vendors on property to sell their crafts to the guests. A few were set up at Grand Lido when I visited there. No hard sells but prices 3x what that same item would cost on the beach at Long Bay) or you might want to try the cliffs. Far, FAR fewer vendors and "hustlers" on the road there.