Well a few considerations:
- You have to size your cooling towers for your hottest hour. Doing this saves you no capital costs.
- You barely have to run the fans on your cooling towers in the winter because the air is so cold. So often this also won’t save you much operating costs.
- Already there is an essentially unlimited amount of so called “waste heat” from power plants and factories. Building district heating systems is extremely capital intensive, which is why this isn’t done more.
- As a municipality it’s just a horrible idea to make the heating system of your whole city rely on a random company continuing to operate (even worse if said company is in a potential bubble). This is why most district heating systems work with power plants - they already have the government involved in ensuring their continuing operations.