Connection between monkeys and diets

I found an interesting article on BBC.

According to a team from the University of East Anglia, there is a close connection between the size of monkeys and diet; mid-sized monkeys are the biggest fruit consumers, and they eat 50 different species of fruit a day. Small monkeys eat mainly insects and larger monkeys prefer leaves.

I did'nt really know that the size of monkeys and foods which they like to eat are closely connected, and moreover, I was even surprised to know that not small monkeys but larger monkeys prefer leaves to fruits or insects. At the same time, I can say for sure that mid- sized monkeys are gourmet, being different from me because, surprisingly, they have 50 different spiecies of fruit. In addition, I remember a problem in connection with the topic. In Japan, especially Nikko, monkeys tend to attack tourists to get some foods, and because of that, people pounched by monkeys get injured, but this is not to say that only monkeys are bad; there are several certain reasons which cause such a situation, so I'd like to ask my classmates about them. (129 words)

Here are 2 questions for you,
1: Can you guess the reason why mid-sized monkeys like to have fruits?
2: Why do you think some monkeys have a tendency to attack tourists to get foods?