[ynfnehf]

ANSI describes why in their rationale: https://www.lysator.liu.se/c/rat/c2.html#3-2-1 .

    The unsigned preserving rules greatly increase the number of situations where unsigned int confronts signed int to yield a questionably signed result, whereas the value preserving rules minimize such confrontations.  Thus, the value preserving rules were considered to be safer for the novice, or unwary, programmer.  After much discussion, the Committee decided in favor of value preserving rules, despite the fact that the UNIX C compilers had evolved in the direction of unsigned preserving.