The cars shape and structural components are designed around the battery. The cars software, motors, charging electronics, software, cooling systems, etc are all designed for the specific battery. The battery eats up a significant fraction of the cost of the car, and the systems designed around it a significant fraction of the remainder.
Asking for interoperable batteries between vehicle brands is like asking for interoperable engines between vehicle brands, it's ridiculous. The government should not be saying "hey, that $xx,xxxx item with a million constrains and optimizable variables, why don't you make it meet this arbitrary standard so people could theoretically put it in another chassis that wasn't designed to let you optimize it as well as possible".
Asking for interoperable batteries between vehicle brands is like asking for interoperable engines between vehicle brands, it's ridiculous. The government should not be saying "hey, that $xx,xxxx item with a million constrains and optimizable variables, why don't you make it meet this arbitrary standard so people could theoretically put it in another chassis that wasn't designed to let you optimize it as well as possible".