1. Economies of scale. The market for an EV is going to be much higher than a whole house battery solution. And most of these solutions are relying on a network of independent contractors to sell and service these batteries. Unlike dealerships, they also aren't buying them at scale.
2. Financing. Most likely you are driving a EV financed by a bank. They've got the process so streamlined you can know within minutes if your 4-wheeled battery bank is coming home with you or not. Trying to get a house battery financed is such a convoluted mess. If it was advertised like a dealership, "Come down to Big Al's Battery Barn. We'll set you up with a 10kWh bank with 0% financing!", I imagine these things would fly off the shelf. Leading back to 1.
2. Financing. Most likely you are driving a EV financed by a bank. They've got the process so streamlined you can know within minutes if your 4-wheeled battery bank is coming home with you or not. Trying to get a house battery financed is such a convoluted mess. If it was advertised like a dealership, "Come down to Big Al's Battery Barn. We'll set you up with a 10kWh bank with 0% financing!", I imagine these things would fly off the shelf. Leading back to 1.