Why did the framers favor the ratification through conventions rather than state legislatures?

Answer 1

Short - many states (esp large ones) would see this new Constitution as taking power from them, and would not be eager to cede that power.

From the spark notes study guide:

"The framers realized that if they sent the Constitution straight to the state legislatures, it would no doubt be defeated, as it took power from the states and gave it to the national government. Additionally, the framers intended the source of governmental legitimacy to be the population at large rather than the states. In keeping with this ideal and with concern for the state legislatures' bias toward rejection, the framers established the system of ratification which eventually took place"
http://www.sparknotes.com/history/american/statebuilding/section7.rhtml


(Note that the "economic interpretation" of Charles Beard--which alleges that the Constitution's supporters acted for their OWN economic interests, with little concern for its affect on others -- a view now espoused by the book cited in previous answer, is rejected by most historians of the period. That is NOT to say economic interest did not or do not motivate people, but that this is not enough, nor should the recognition of SOME economic factors make us cynical. This is NOT about some ivory tower ideals, but about what they thought would work in their REAL situation. Insofar as economic factors affected decisions, may we not also presume the OPPONENTS shard such motivation??

Of course, that particular view does not quite answer the question. Even following such a view, the answer given above could still apply.)

Answer 2

The framers and ratifiers of the Constitution were less interested in furthering democratic principles than in advancing specific economic and financial interests.
http://www.oup.com/us/catalog/general/subject/?view=usa&ci=0195139704