Comment by AngryData

It is primarily the forward sweep/caster of the front wheel forks which makes the wheel turn into any lean and the forward motion of the bike with the turned wheel tries to bring the bike back under the overall balance point. With the steering axis/forks in a perfectly vertical position where the wheel's contact point and steering axis are perfectly aligned, the wheel will not really respond to leans and you would have to actively turn it to balance. And with a negative caster the wheel would want to actively turn away from any leans making the bike fight against balancing.