All reasons are legitimate. But with proper action all can be addressed and diminished. They weren't in Poland. So now we are drowning in traffic and parking issues just like everybody else despite superior dwelling style.

You asked why Polish people bought cars if they didn't need them.

The answer is that they started needing them. Large shopping malls popped up on the outskirts of cities not easily accessible without a car.

Trains and other mass transit didn't really improve to meet the demand for travel from richer populace. Often it deteriorated. People were forced to substitute public offering that didn't keep up with private car ownership. Public enterprises are hard and when the government fails people invest in personal facilities to get by.

People buing cars is a sign of the community dropping the ball on the mobility needs of the people.