Why does female anatomy always get used as an insult? It's a prime example of toxic masculinity and patriarchy that non-male genitalia are so reviled as to be an insult against others.
You use whatever is gonna make the target mad as an insult. It's why bad mouth little kids will go after your mom or say removed in comms. It's the low hanging fruit. They don't care about your mom and they're not likely to be racist either. It's about attention.