Would it have been awesome for Zach to learn from the great Andy Reid who has proven to be a QB whisperer? Yes, that would have been awesome. But that dream scenario didn't work out and didn't make the most sense for the Chiefs, especially given Zach's single year left on his contract.
The Broncos are drafting a QB. They are looking for a placeholder while they bring their rookie along. Enter Zach and Stidham. One of them will earn that job. Zach has an opportunity to earn that job, do it decently under a coach who has proven competent with a QB friendly offense, and therefore rehab his currently in the trash NFL value in a contract year.
Unless Zach lights the world on fire, this is a 1 year stint in Denver. That's all they want him for. If he plays decent, then Zach will be able to sign a decent contract somewhere else next season.