I understand that but there must be a reason why Много takes genetive case. This adverb must be the genetive form of a word. Maybe it has the nominative, the accusative, dative etc equivalents? Like in English (if I am not mistaken) "lot" means "many of something". So it is used as "a lot of cars". My point is "a lot of" in English has a reason for the way it is used so Много must also have a reason.