These also don't disappear if you replace privately-owned cars with buses and trains. You need paved roads to put buses on and track to put trains on, and they emit particulate pollution as well unless they're also electrified which is a similar problem to electrifying cars.

Low-density residential sprawl is mostly water-inefficient because it allows people to have the ability to have a garden that they water, you don't inherently use more household-internal water if you live in a suburban house compared to an apartment. Most of the energy efficiency issues are also directly related to low-density residential zoning allowing for more physical space for a dwelling than an equivalently-expensive dwelling would cost in an expensive, dense urban area. In short, the things about low-density residential neighborhoods that are less energy efficiently mostly don't have to do with cars and mostly do have to do with goods that people actively want and can only afford outside of dense urban areas.