Alotta Bronco fans around here want Cousins in Denver. Plus when it comes to drafting QB's Elway so far has been terrible.
I know what the sentiment must be in Denver, however, there's a reality that comes with signing Cousins to a deal that's going to be competitive with what he'll command and maintaining the competitive edge that Denver currently holds.
Beyond that, Elway is known to be a pretty frugal guy when the question is paying or rather overpaying QB's. I believe that he's sold on Mayfield and is more likely going that route instead of chasing Kirk. There's an energy to Mayfield that Cousins simply doesn't have, that I also believe Elway wants to bring to the Broncos offense.
No doubt Cousins would be a nice fit in Denver and while I don't disagree with your assertion related to what the fans want, the terrible Elway drafting QB's, IMO will do exactly that for the reasons stated.