Earlier quoted context omitted.
Thermal power plants generate lots of waste heat that can be used for district heating. If you don't use that waste heat it will still be there. Worse if you need electricity for cooling you end up with even more waste heat. Your assumption falls flat because a lot of people don't need to generate extra heat from electricity, they already have too much of it.
First off, AC is a heat pump, and heat pumps are always much more efficient than direct heating. A well designed AC system can be up to 500% efficient, since it only needs to move heat and not generate it. Secondly, municipal heat is pretty rare in the US; few cities have it and the number keeps getting smaller each year. What few municipal heat systems that do exist are largely for business districts too, unless if…
I'm assuming by "municipal heat" you mean district heating. Can you explain why those systems keep getting rarer in the US? Over here in Europe, we are investing a significant amount of money in expanding those systems and connecting more houses.