The simple answer is that WN can't generate the PRASM serving both IAD and DCA and so it serves the one with the higher PRASM. That is generally DCA for O&D traffic. Not to suggest that there is not a market to the Dulles corridor, simply that it's not the same. So, I would not look to see IAD service restored.

However, OP says "Western Virginia." Thet can mean many things. Is it possible that RIC is closer? Any other airport? Why not provide the name of the specific destination and the advice could be narrowed down.