Imagine the electrical demand on the grid during a cold snap if everyone switched to heat pumps with resistive heating as a backup. At the time of largest demand, the largest electrical appliance in each home would be reduced to a fraction of its normal efficiency. And all the homes in the region would be experiencing that same thing at the same time.

Electric resistive heating is not a suitable backup. If adopted at scale, it would tend to amplify demand spikes when the grid is at its most vulnerable.