"What's going on? Not much."
Translation:Dè tha dol? Chan eil mòran.
Why would it? Would you say in English not big; big isn’t (going on) in that meaning (as that’s what chan eil mòr would translate to)?
Much, a lot (as a noun) is mòran, not mòr (that’s just the adjective big, great), and thus not much is (going on) is chan eil mòran (a’ dol).
Think of it as a lot in English (or a great deal, or multitude). Lot is a noun, and in the phrase there’s even the indefinite article (that comes only before nouns), a, in front of it.
Because of that mòran is followed by genitives (similar to English a lot of somethings, a great deal of somethings) or prepositional phrases with de ‘of’ (even more like English a lot of…).