The article says it was a mandate from Elon Musk. Not sure I believe the claim, but I'd also be surprised if he wasn't aware just how optimistic the EPA estimate is.

My initial thought is that it's a mitigation to litigation. Maybe the thought was as long as you show the "legal" mileage calculation, you can't be held responsible for anything bad that happens? I don't think we apply that to ICE but I could see where a lawyer thinks it's necessary.

I think you need to give consumers some vague idea of how much range you'll get in the car, and EPA-rated miles is at least a clear standard by which all EVs can be compared.

A percentage indicator is fine for a car you already have, but not useful for comparing between cars. It could show kWh, but that isn't good, either. What consumers actually care about is range, and whether that comes from more kWh, better aerodynamics, or a lighter car, the range is the bottom-line number. We wouldn't want consumers buying a car with a bigger battery just because it has more kWh if it doesn't get better range.

I think EPA-rated miles is the best of available options--it just needs to be understood by consumers. And I think cases where it isn't are a bit overstated. I suspect very few consumers genuinely believe they'll get the same range in miles regardless of their driving speed, headwinds, or whether they're going uphill or downhill.