Why do some people put milk in tea?

I’ve been seeing some questions about putting milk in tea before or after you make it. Which made me wonder.
I’ve never put milk in tea before and don’t know why anyone would do it… Seems like it would taste really funny.
But I drink sweet tea (tea with just sugar added to it) and I’m not sure if it’s because most northern people don’t drink sweet tea (so I’ve heard) or what.