Part of that development delay is the deliberate decision of the US (and other countries) to build the types of reactors that can produce weapons grade plutoniu

Part of that development delay is the deliberate decision of the US (and other countries) to build the types of reactors that can produce weapons grade plutonium - for the express purpose of using it for nuclear weapons. Nuclear reactors are crazy expensive, so if the money comes from people who want Pu, then that's where the R&D goes.