Why you may ask? Simply because the iso contains a file larger than 4GB (install.wim) so you cannot use a FAT32 formatted usb drive (FAT32 is needed for EFI boot). Instead tools like Rufus provide their own EFI NTFS boot loader.
Interestingly Microsoft’s own usb creator doesn’t include install.wim but instead install.esd which is less than 4GB so can use FAT32. I have no idea why the iso uses a wim file whereas the windows usb creator uses an esd file. I do know the esd version is a little slower to install (only a minute or two). I guess because of higher compression.
This is a pain because making a Windows bootable installer on Linux or macOS is now more complicated than it need be as you cannot simply put the iso onto the usb drive with dd or gdisk as you would normally do.
Does anyone know why this is the case? As a workaround you can use Microsoft’s usb media creator to build an iso with the esd file then use dd as usual. But of course this requires a Windows system to run the Windows only usb creation tool and is a slower process than just downloading an iso directly. Annoying.