it's the same reason that convex mirrors in America must have the text "OBJECTS IN MIRROR ARE CLOSER THAN THEY APPEAR" engraved. i.e. Americans (think Americans) are stupid.
Precisely.
S5.4.2 Each convex mirror shall have permanently and indelibly marked at the lower edge of the mirror's reflective surface, in letters not less than 4.8 mm nor more than 6.4 mm high the words “Objects in Mirror Are Closer Than They Appear.”