I drive a semi , if i am driving at the speed limit , why do people exceed the limit to get around me & brake?

& break HARD ! i cannot stop 47 ton instantly. i am scared of crushing people. in my observations, the worst offenders are young females in little jelly bean cars , the elderly & any one in a volvo. am i alone in my obs ? i am not a cowboy, i am calm a & cruisey operator.