At a certain point in EE power design you don't really want to go from 54V -> point of load for every rail (1.8V, 1.1V, 0.9V, SVI3 rails etc), so sticking with an intermediate voltage makes sense often even when viewing this from an efficiency perspective. Voltages such as 54V require different creepage and clearance requirements, so saddling every point of load regulator (of which we have many many!) with those requirements is often detrimental to an already complex board layout. Picking something like 12V or 24V as an intermediate voltage helps balance those requirements with the amount of copper you need for power delivery since the parts use low voltages but are extremely power hungry so your current at the point of load rail is a lot. This also means that your point of load regulators have to be distributed around the board near their loads otherwise the copper losses and noise would become problematic.