Why do people like to shit on each other's music taste?

because they want to feel like they are the only one thats special

because only satan worshippers enjoy listening to Cardi B.

I get this all the time when I post rap music 😂

I do it as a joke to friends but I honestly don't care about music tastes.

Exactly

It goes to the idea of cultural capital. That your taste in music is like a currency that buys you access to certain social spheres.

All the fancy rich people like a certain kind of music and art, all the punks like another, or the emo kids or whatever.

And when people are shitting on other peoples' music tastes, they're trying to establish a kind of social hierarchy with them on top. "I hate country and rap" is code for "I hate music I associate with poor and/or black people because I am of higher social standing" even if that's not even conscious. Or like teenage boys hating on boy bands - that's just sexism and trying to claim things women like are frivolous and without value, like whatever shit they listen to is any better.