It's pretty simple, putting someone else down makes you feel powerful. That's really all there is to it. It's the same kind of thing kids do when they kill random bugs they find, they're asserting their power over them.

I know nothing about you, but there are probably analogues in your life as well:

• bragging about a good score in school
• comparing how many books you've read vs others
• comparing your income to someone worse off

Basically, you want what you have to feel better than what someone else has, because that means you're "better" in some way. It's just pride at the end of the day, and not a constructive form of it since you usually feel worse afterward.