The reason the high voltage battery is isolated while parking is safety, every time a car with a high voltage battery pack is parked the battery needs to be safely cooled and stabilized. The low voltage system is kept running to monitor the high voltage battery and insure that it remains stable. Some people do not realize the volatility that happens in an automotive grade lithium ion battery pack, but it is serious and must be monitored. Bolt EV battery fires are a good example, not a single Bolt caught fire while it was being driven, and coolant circulating, fires happened after charging, or while parked. These are times the coolant flow is stopped, and if a single cell overheats the BMS does not always sense it and restart the cooling. I have noticed my Tesla the cooling system often runs 20-45 minutes after the car is parked or charged, where our Audi E-Tron does not do this... In the Audi, when charging stops the the cooling system shuts down. I hope the later generation EV's have better monitoring, and sensors to babysit the high voltage battery pack, and fires should happen less often.It's not about affordability, it's just no practical. You wouldn't want the main traction battery always connected. You might go to higher voltages for the types of things you mentioned. Something like 48V, but no one is talking about 400V.