The wiring for 48V can be a lot thinner than it is for 12V. As there is a square law involved for resistive heating it turns out that wiring for 48V can use 1/16th of the weight of copper as that for 12V.
A switchmode converter can be designed for 48V just as easily as 12V.
You generally can't reuse non-automotive power supplies in automotive because the requirements are very different.
Hobbyist computing could benefit from a move to 48V as well, if only to keep the problematic 12VHPWR from killing expensive video cards.
I say hobbyist because AIUI 48v is making inroads in server hardware but that's not my area.