The question is not whether you could dump Lock on the market - but why do it now - instead of months ago? The path of drafting a QB now and trading Lock at the same time or later -- is incoherent as a strategy and a waste or resources. If Lock wasn't going to make it as the Broncos QB - and the front office knew that months ago - that was the time to trade lock for maximum resources. Trading lock as you maneuver to draft a new rookie QB - is a waste and is not consistent with the free agent signings of veteran players that took place - as there has to be some idea that the new QB will need to learn something on the job.QB's especially young ones will always hold value. Sam Bradford got a 1st round pick late in the offseason even though he had been average at best in his career. Darnold, who played maybe worst than Lock, just got huge return.
You will always find a team willing to give something up for him. Let's say the Steelers miss out on all of their QB targets to replace Big Ben. They could trade a 3rd round pick and have Lock sit a year then see what he is the final year of his deal. The great thing with Lock is even if he doesn't play he is a quality back up and cheap. That is still worth something to NFL teams.
For me personally I don't think the Broncos are just trying to push Lock. People I've talked to say their love of a few of these QB's is real and if given the opportunity they will trade up. They have competition and Paton has shown he is not going to go crazy in any trade so we shall see. The nice thing for the Broncos is their competition all are teams pick 15 or later and most teams in the top-5 don't like the trade back that far.