They are pretty common in passenger cars too, google 'standheizung' or 'stationary heater' and you'll find a ton of them. You might not realize that that is what it is. On cars sold in the Nordics and some German brands it is just a checkbox during the order process.
It's quite normal in colder climates, but mostly in Diesel cars. I had it in my VW Multivan. I've never heard of anyone installing Webasto in their EV.
