Why are girls so unfriendly and don’t say hi back?

I get it that I may be a stranger but it’s common and normal for people to be friendly. Every time I walk by a girl near my college, I would just say hi because I am polite and being friendly but they never say hi back. The girl would just stare, ignore me, and give me a weird look. It’s like you can’t even say hi to a woman these days anymore without being accused of being a sex offender or hitting on them. Is it too much to ask for someone to be friendly and say hi back? It’s not I am asking to date them.