I don't argue the importance of being listed on exchanges, by the contrary. I guess you need to ask yourself why a joke coin like Doge managed to get listed on so many exchanges while Mastercoin didn't have much success in doing so. Perhaps it's an issue that needs a quick fix.
As the maker of an exchange that accepts Mastercoin, I'd say Dogecoin is accepted on so many exchanges because, as a clone of bitcoin, it requires almost no workload to add to an exchange that already trades several Bitcoin clones. Mastercoin on the other hand, requires specific development for deposits and withdrawals, and there is no official client yet. No amount of marketing will change that at this point.