The review panels that score grants at the National Institutes of Health (NIH) are comprised of professors. (Mostly; being a professor isn't technically required.) If a proposal is scored well by the review panel, it is almost always funded. The National Science Foundation (NSF) works similarly. If (a) the review panels were on board with duplication and (b) people started submitting proposals for duplication research, those proposals would probably get funded.
Edit to clarify: The point is that professors, as a group, already have the power to allocate funds to duplication research if they wished to do so. Blame for a lack of duplication research cannot be pinned solely on the funding agencies.