It doesn't have to be price or ideology driven (though it can be). It's the rational choice for a lot of people. When a car is the slowest form of transport, costly to own, and you can rent/borrow a car for the very few occasions in the year you need to have one, it doesn't make sense to own one.

Add to that that a lot of young people in big cities don't even have a driving license.

Obviously it depends a lot on where you live. A lot of places in Europe still require you to have a car to get around.