"work where they live"- a good point. The way most cities develop in the United States and Canada mitigates against efficient mass transit. New York is relatively good; to a large extent transit grew as the city grew. I think some of the other NE cities are good.
Many cities are playing catch-up, they have grown many miles in all directions and city fathers kept taxes low to stay in office, but infrastructure costs were constantly increasing. Now an efficient city is beyond the means of the citizens.

Many major European cities are compact- I remember starting out on a walk from Brussels city center, and it was not long before I reached the outskirts and farms. In the new western city of Calgary, I could walk all day before I reached the end of the suburbs or industrial districts, depending on the direction I took. Little more than token expansions to mass transit are made because the citizens and the aldermen look at the bill and back away, so one continues to drive miles to work. To get away from the city, bedroom communities have developed outside of the city limits. Houston was very bad, some people who worked where I did drove many miles and an hour or more to get away from the 'dangerous' city and schools with low standards- buses ran infrequently, mostly to get maids and illegal immigrants to their chores.

Perhaps sophisticated communications, allowing many people to work at home, plus mass shopping from on-line stores to reduce trips to malls- dunno.