A lot of Londoners don’t own a car. I own a car in Portugal, but when I’m here I don’t feel the need for one (plus all the headaches and bills it brings).
I would say it’s because you can go almost anywhere easily by public transport (and sometimes faster). I find public transport is quite reliable and frequent (most of the times), as opposed to Portugal.
I like the freedom of not having a car (even if I still have to pay my car’s insurance every year…).