You're right, heat pumps have been around for a while, but they're only at 15% market share across the whole US. The Southeast, for a few different reasons, has the highest market share. (1) It doesn't get that cold, and magnitude of heating/cooling loads are close enough that single stage equipment provides an OK experience. (2) There's very little natural gas infrastructure.
Cold weather heat pumps have recently become popular and enable increased adoption in the northeast, and the fact they're so efficient means they're competitive even in areas with a lot of natural gas infrastructure.
Cold weather heat pumps have recently become popular and enable increased adoption in the northeast, and the fact they're so efficient means they're competitive even in areas with a lot of natural gas infrastructure.