Being a displaced New Englander I'll take an unscholarly stab at this - I think a number of things account for the lower volume of regional north east tunes - (not sure about north central) - lots of gross generalizations here so I know there some issues to take with this -
New England was initally populated by religious groups who were not into frivolity a whole lot. I think it took a lot longer for music in New England to overcome that than in other parts of the country. Hymns were OK, sea chanties and whaling tunes were ok for the right context, a good war could bring on some good singing to commemorate a battle - but to just make up and sing or fiddle a tune about some little local place or event was not in their nature. It happened sometimes but it was not a daily encouraged event. I seem to recall Lomax having a section on the North east including things like In Good Old Colony Days, and Blow Ye Winds, so there were a few. A number of others have been mentioned previously in the thread.
Cities also grew up early in the northeast and urban music and performances of european music were of more wide spread influence than in the more rural and more spread out rural and mountain states in the south. A higher percentage of people in the north east lived within a day or two of a major city in the north east than in other parts of the country - and the railroads were established earlier there. For many north easterners was much easier to go hear "performed music", they didnt have to make up there own.
Contrast this to the south and other more isolated rural areas where tunes were made up to pass the time over incredibly mundane things - Old Yellow Dog Come Trotting Though the Meeting House, Possum on Rail, etc. Every southern, mountain and midwest rural community had their fiddler and would have dances where these local tunes would get played (plenty of non mountain midwest tunes -Big Sciota, Dubuque, Old Jeff City, Going Down to Cairo)- that was not the rule as much in New England where dances, when permitted were more inclined to be more traditional waltzes.
New England also did not get the early "benefit" of the infusion of music from slaves and free blacks, who were much greater numbers in the south - including the banjo, spirituals, early delta blues etc. There was a lot of fusion that went on in the south before a lot of this influence drifted back to New England following the Civil War. A lot of these tunes were related to local conditions and places and self entertainment.