Whenever we talk about the character of some place and how it came to be, we are necessarily guessing or speculating. There is no way to definitively prove why the character of a region (to the extent that it truly has such a thing) came to be.
The most common answer for this would be that the character of New England came about because of its Puritan and family-oriented background. These are the things that made New England different from the other colonies.
Because of these factors, for example, New England came to be an egalitarian and educated area. The Puritans did not believe much in hierarchy and they did believe very strongly that people needed to be educated so they could read the Bible. Because of Puritanism and the large number of families, New England came to be a more sober area without the flamboyance of places like the South.
From these factors came the hard-working, sober, egalitarian nature of New England.