I think the answer is simply that if you run the numbers, it's just not economical to use nuclear plants for district heating. It's probably great if you can us

I think the answer is simply that if you run the numbers, it's just not economical to use nuclear plants for district heating. It's probably great if you can use district heating for cooling, but generally nuclear plants are very expensive so you want to get as much high-valued electricity out of them as possible.