With the car, you know way in advance how much fuel you have and so can plan your journey accordingly. If despite knowing your fuel reserves, you still end up in a situation where you run out of fuel in the middle of the road, then that’s really on you.
With the iPhone, there is no way you can know when your phone is going to shut down on its own and preemptively turn on low power mode to prevent this, so it’s something which has to be on 24/7. What Apple is doing here is to have your iPhone intelligently manage its power consumption automatically behind the scenes to avoid a shut down so that you as the user don’t have to concern yourself with nitty gritty details such as this.
The entire point of simplicity isn’t to do more with more, but to do more with less. We use Apple products because we trust Apple to make the right call with regards to decisions like this, and given that Apple was basically stuck between the devil and the deep blue sea, I do honestly feel that they made the better call overall. Both options sucked, and so Apple chose the one which sucked less.
I suppose an argument could be made about how Apple should have been more forthcoming about this, but I can understand why they decided to maintain radio silence. There’s really no way to nuance this without people misinterpreting and taking the news out of context.