Question

why do people make fun of those who are different

Answer 1

Not everyone does that. Some people like making fun of people who have lesser than them or people who are a little timid. Sometimes, they are jealous of what they have and start bullying them, which is not good. Also, most of the times people don't have a good perspective of viewing themselves, so they think that making fun of people who have lesser or different will make them feel better. They are even made fun of because of their body color, shape, or any unique attribute they've got, again probably because of jealousy, But instead of that, helping people who have lesser, behaving softly with them, and praising them (don't tell white lies) would make them feel better.

Answer 2

not all do but some do it because they all are of little  mind and they think themselves as superior