Why are American people a lot more friendlier and chatty than us English people...?

I'm not saying British/English people are unsociable, but not many people over here tend to start a conversation with you. I have noticed that when I'm out and about, people just don't acknowledge one another, they just look miserable and wary all the time. When I went to New York and Texas last year, loads of people wanted to get to know me, they would chat loads and be really sociable. I asked someone about why they are so warm and chatty all the time, and this lady told me that they are always like this, and it wasn't just because I was a foreigner. In the UK, if I went up to someone and asked them a question, they look at you as if you're an alien or something. Even when I go up to ask someone the time, they give me a look that basically says "Why are you bothering me" and it's stupid right? I like to get to know new people, especially people my own age (I'm 23). But people just don't seem to want to give you the time of day, well few people anyway. It's like everyone is in their own little bubble, comfortable with their own close knit group of friends, and don't want to break out of that bubble.