In my opinion that would eventually make searching for a free item in the forge a nightmare. Everyone would try to charge for any behavior in there, and there are plenty of simple ones that should not have a fee attached to them. Not to mention the amount of duplicates that exist and the amount of work that would have to be done on Stencyl's end to allow selling assets/behaviors in the forge.
People can still use the forums to try to sell assets or extensions, and they can use the Payed Work subforum to request for behaviors.