Internally, NT first targeted Intel i860, not x86. This was a deliberate decision to break old assumptions. It was designed to be multiplatform from the beginning. The fact that it had an NT syscall layer but also a Win32 one, then formerly an OS/2 subsystem, also reflected this heritage of adaptability, multi-platform, portability etc.

Mostly because that format is not strictly speaking Windows-specific but comes from Unix System V release 4. Also various oddball embedded platforms use the full NT-style PE COFF as their native object/image format (but these usually either specify i386 as machine type or place some invalid value there).

That is controlled by this bit in the subsystem field. https://learn.microsoft.com/en-us/windows/win32/debug/pe-for...

Subsystems https://learn.microsoft.com/en-us/windows/win32/debug/pe-for...

There are also a few others usually NE for older win16 and LE for OS2 and other interesting win16 overlay types.