But the point of a language is not to spread to the most people, it is for the peoples using it being able to use it in a way that makes it possible to communicate with their own in a way that makes sense within the local population, its culture and history.
Different languages have a different learning curve based on what language you grew up with. What is hard for you might be a cakewalk for someone coming from a different language, especially if you are coming from a different family of languages.
You can't walk in a car filled street. Look up walkability and you'd see walking, cycling and trams sharing the same space. And using 8 sq meters per person is just inefficient transportation in a city with a lot of people. That same space could transport at least 10 people on the same space.