If we want to know why we can never again replicate the extraordinary generation of the founders, there is a simple answer: the growth of what we today presumably value most about American society and culture, egalitarian democracy. In the early nineteenth century the voice of ordinary people, at least ordinary white people, began to be heard as never before in history, and they soon overwhelmed the high-minded desires and aims of the revolutionary leaders who had brought them into being. The founders had succeeded only too well in promoting democracy and equality among ordinary people; indeed, they succeeded in preventing any duplication of themselves.
That is from Gordon Wood’s new and excellent Revolutionary Characters: What Made the Founders Different. It is in my view the best introduction to the lives and thoughts of the Founders.
I don’t, by the way, agree with the above quotation. The Founders were not the smartest Americans to have come down the pike. Instead they a) were extremely wise, and b) had a unique chance to be both great and famous because they were first. It has not exactly been a string of mediocrities since then, and of course there is more to American life besides the Presidency.