I don't understand how the population demand circles are determined

I don't really get it. Sometimes there is a dirrect line, from the place they live at, to the place where they work and they still rather drive. Even when the workplace and home is like right next to the station. It doesn't even take that much longer for them to get there compared to driving, it's like 17 minutes difference.

On the opposite side of the spectrum, I've seen pops who live like a kilometer away from the station take the public transit even though it takes double the time of driving - like even differences like 30 minutes driving 60 minutes on the metro.

So what determines whether the pop demand for transportation is met or not ? It doesn't seem to be the distance to the station necessarily, it doesn't seem to be the time it takes to travel or how many times you have to transfer. It doesn't even seem to be the ticket price, since mine is set at 2.50 and the parking price alone is double that, so what gives ?