Is it normal here for neighbours/people to not greet each other?

I moved to Pittsburgh and the US about a year ago, and I still can't figure out this thing. Is it normal for neighbours to not respond when you say hello and smile? I come from a country in Europe where greeting neighbours and acquaintances is considered polite and even mandatory. The only time you wouldn't respond is if the other person has done something really bad, like insult or humiliate you. As I'm writing I realize I have this situation only with women (I'm f). I live in an apartment building and it's pretty consistent. One of the neighbours is someone I've texted with over practical/building things and she completely ignores my hello. There is another woman I see almost daily in a group setting, I intensely lock eyes smile and wave and she ignores it. In other instances she talks to me, I just can't figure it out. It happens at work too, when I enter a room with people in their early 20s I say good morning and they don't respond. This would be considered extremely rude in my country - to either not greet someone saying hello or to enter a room without saying hello. Is it not the same here? It's difficult not to get paranoid about it because of my cultural background (I'm white but have an accent so probably obvious I'm not from here). It's hard not to feel rejected. So what's going on?

Edit: Thank you all for responding and reassuring me! All I've read here definitely helps change my perspective. That being said, I'll keep on being myself and greeting folks. And I don't lock eyes intensely, I meant intently, but it's funnier like that :))