Because it doesn’t solve the problem, it merely works around it. Solving the problem would mean coming up with a battery chemistry that doesn’t suffer in the cold. Instead the answer is “just don’t have it get cold”.

It’s not to say a hack/workaround isn’t useful, and I would say that it’s perfectly acceptable to simply use a battery heater in the winter. But calling it “solved” confuses solutions and workarounds, and that’s an intellectually dishonest thing to do.

Leave your car with 5% SOC overnight and then try to find energy in morning to preheat battery. People have painted into corner themselves before. It’s perfectly adequate for my very mild climate and even then I get limited regen about 6 morning months per year.

It takes hours to heat a cold large pack til it's warm enough to charge. That's a drawback.