This is because "Hace mucho mal tiempo" translates to "It is very not good weather." All the other options are positive options, like "Hace mucho sol" is "It is very sunny", "Hace mucho viento" is "It is very windy", and "Hace mucho calor" is "It is very hot". "Hace mucho mal tiempo" is wrong because it is negative, and because you can't put two Spanish adjectives together like that. This is right on edg2020 I SWEAR.
