It's fast, and now it's cheap. Low-cost air travel is enticing people out of their cars. Saving travel time is the biggest motive, of course. But some airports get low marks on this. They aren't convenient, quick, and enjoyable.
Some airports require check-in times longer than many of their flights.
Once again, it's an airport designed in response to human needs and limitations. Nearly all humans seek to enjoy life and life's experiences. Most values are obvious. All things being equal, they always choose quicker service and lower cost. People remember enjoyable experiences, and plan their travel accordingly.