There is nothing inherently convenient about cars, or about any vehicle. It is the system that makes them convenient, and that system includes both the vehicle and the infrastructure. Provide unlimited, subsidized "free" car infrastructure, and cars will be convenient. Run buses often, everywhere, all the time, and buses will be convenient. Put everything in a giant skyscraper with computer-controlled elevators, and elevators will be convenient. Trains, walking, bayou boats, swinging from vines, conveyor belts, scuba diving: whatever it is, if you throw enough money at the infrastructure you can make it convenient.
-- Cap'n Transit, "On the Supposed Convenience of Cars"
You have to go back to the urban limits of old pre-automobile cities with intact transit systems to understand how significant this is. Manhattan doesn't have a big subway system because of the density--Manhattan was once much less dense. It big subway system because a) The subway system was too big to fail, and b) it didn't compete with cars for Right of Way.