Another factor: they haven't given up on Paxton Lynch.
Peter King of The MMQB reported general manager John Elway still has some level of regard for Lynch, who they selected in the 2016 first round (No. 26 overall). Lynch's first two NFL seasons have been a bust, with the 6'7" signal-caller attempting just 128 total passes.
"I think Paxton is a factor," Broncos head coach Vance Joseph told reporters last month. "Paxton's had four, five starts, and to deem Paxton not capable, that's not fair. Obviously, it's an age of instant gratification for all of us...but it takes time to [be a] good quarterback in this league. I think once Paxton gets more time he's going to get better as a quarterback. By no means is Paxton Lynch done. By no means at all."
King's report also said Elway does like a quarterback in this draft, pointing in the direction of USC's Sam Darnold and Oklahoma's Baker Mayfield. Darnold will almost certainly be off the board by the fifth pick. Mayfield could be available and tempt Elway if, indeed, the Heisman winner is the favorite of the Hall of Fame quarterback.
Denver also has Chad Kelly on its roster. Kelly spent all of last season on the non-football injury list. The Broncos selected him with the final pick of the 2017 draft, and he could be a threat to make the roster over Lynch if the two battle in training camp.