Then the graphics card would have to have a transformer on it to step down to the voltage that the chips can handle.
You'd probably use an intermediate 12V rail especially since that means you just reuse the existing 0.8V regulator designs.
There are other issues, too. 48V would fry the GPU for sure, 12V often time does not even with a single power stage failure.
In the end we are talking about a stupid design (seriously 6 conductors in parallel, no balancing, no positive preload, lag connectors, no crimping, no solder) and the attempted fix is a much more sophisticated PCB design and passives.
Your SMPS needs sub-2V output, cool. That means it only needs to accept small portions of the incoming.
But, if the incoming is 48V, it needs 48V tolerant parts. All your caps, inductor (optional typically), diodes, the SMPS itself.
Maybe there isn’t a sides difference in a 0603 50V capacitor and 10V 0603 capacitor, but there is a cost difference. And it definitely doesn’t get smaller just because.
Your traces at 48V likely need more space/separation or routing considerations that they would at 24V, but this should be a quickly resolved problem at your SMPS is likely right next to your connector.
Extra insulation is likely only a mm or two, those other components are big and heavy, and have to be.
It’s the same reason inverters have been moving away from 12v to 48v. Larger currents require physically larger and heavier parts in a difficult to manage way. Larger voltages don’t start being problematic until either > 48v or >1000v (depending on the power band).
It doesn't look to me like anything out there can take voltage from 48v to 2-3v; at least not obviously.
There should be plenty. 48-54 VDC is the standard for OCP powershelf designs. Hyperscalers such as Google have been working for nearly two decades now to eliminate voltage conversion steps. When I left, the power plane within the server PCB ran at the busbar voltage, which could float up to 54VDC. Given this, I'd expect them to convert from 48-54VDC down to 3.3 directly or at most something like 5VDC and then use smaller VRs near components such as ram and cpu.