In warmer climates, electric heating has always been common, and usually very inefficient forms, like electric baseboards.

What your saying is all true and it’s probably a factor, but I’d bet it has more to do with the fact that the cold really widespread and so there’s a lot of “warm” places using electric baseboard heating (and space heaters) than it is an uptick in housing using heat pumps.

And there’s also a bit of a mix where some heat pump systems have resistance heat backup systems for when it gets really cold.