[T.B. Yoits]

That only applies to Southern states. A lot of Northern states have greater power demand in the winter and it doesn’t actually fall off much in the summer.

I recall that heat energy in northern states is mostly from oil, natural gas, and propane. Electric heat is less common and an as such requires much less electricity generated compared to air conditioning, so power companies take the generating stations off-line during the winter for maintenance to prepare for summer demand.

[Spktyr]

This has changed in recent years as with new build homes and new regulation there has been a massive uptick in electric-only heating in many areas.

Also, heating is actually more energy intensive than air conditioning IIRC.