Yes, it's cultural. It's also part of the 'loneliness epidemic' that is affecting most westernized countries. As a larger and larger cohort of the population becomes socially isolated, especially young adults.

And frankly, I've noticed a huge cultural shift in my own city the past 5 years. I used to have way more casual interactions, and now many of those same casual interactions are viewed with hostility and suspicion... just like OP's reaction.

10 years ago if someone dropped something and you picked it up for them they'd thank you. Now they act get angry with you for trying to help them, and sometimes accuse you of theft or harassment. And that type of reaction basically teaches folks to just not bother, it's a type of death spiral. Even personally, as the years go by and the hostility ratio goes up, it makes me increasingly want to socialize less in general. Even many of my closer friends from years ago have gone down this rabbit hole of hostility and suspicion, and I stopped interacting with them because it was so exhausting and miserable to be around someone who thinks the bartender is 'looking at them funny'... no it's you whose looking at the bartender funny... you idiot.

It is increasingly difficult to find folks who are receptive and open minded to strangers, which is the building block of any/all socialization. And what's incredibly rare is folks who can just politely say no without demonizing the other person.