Proper cities are designed for sustainability not for walking only , Dhaka is a failure in all aspects of being a clean , well planned out and sustainable city.You don't know anything about urban planning anyways. Designing a city around cars is dumb and has never worked just look at the US and China to some extent. Streets should be narrow just look at cities in the Netherlands. Density is always good and a million times better than sprawl. "Smart city" is an empty buzzword that means nothing. The city is being designed around walking and not multiton hunks of metal with ACs in them
As time goes on and the socio-economic situation of a city improves a lot of people end up buying vehicles , so cities have to also plan for cars.
Also narrow streets ? I mean I live in NYC and streets aren't super narrow lol , just narrow enough to park cars on the side but have room for cars to drive either ways