Rapid chargers are primarily a psychological safety net. Prospective EV owners really worry about them, but EV owners rarely use them. You might take a road trip once a year, but the average driver covers less than 40 miles per day. The normal overnight charging that represents the vast majority of EV power consumption is actively beneficial to the grid by providing demand smoothing; the marginal cost of a kWh falls if someone is willing to buy super-off-peak power at 2am.
Superchargers are almost always full where I'm from, even in shopping malls. I'm sure they'd be even more commonly used if more of them existed. People just know they can't rely on them yet in the same way they rely on finding a gas station
