yencabulator parent
We're talking about the accessory battery in a car, though.
We're talking about the LV rail (nominally 48 V or 12 V) in an electric car. There are two design paths here -- you can have an HV to LV converter capable of supplying the average load, and have an LV battery; or you can have an HV to LV converter capable of supplying the peak load, and save the cost, weight, and failure rate of an LV battery. Tesla chose the former, but it's not the only path here.
Sure, in an EV it's possible to choose not to have that second battery. In an ICE car, it's needed to start the engine. So at least the ICEs are much more likely to settle for 48V than something closer to 60V, to leave room for charging. The manufacturers that make both ICEs and EVs are going to want to share components, so the pure-EV components are likely going to be built for 48V too.