Thousands of industrial machines (CNC routers, MRI devices, gas chromatographs) still run on XP. The manufacturer either went bankrupt or charges $10,000 for a driver update. With a Windows XP Portable USB, a technician can boot the machine, run the diagnostic software, and leave the host OS untouched.
Creating a bootable USB version of XP typically requires specialized utilities to handle the "text mode" and "graphical mode" installation phases. airfiko - Blog windows xp portable
Use Win10XPE (ironically, a builder for modern PE) but if you want pure XP, use WinBuilder with the "NativeEx" script. Thousands of industrial machines (CNC routers, MRI devices,