I would guess "because people complain when it gives warnings related to macros." That's almost always the answer, especially for C.

I wonder the same. Especially because this might be the same code that deletes null-checks as an 'optimization due to undefined behavior' as discussed here [1].

I recall a bug report with quite the flame war in it, but couldn't find it.

[1] https://kb.isc.org/article/AA-01167