I think what the Jazz do is take a high-level view of the draft and decide who it is they want. They don't start from the perspective that they're drafting at #21 or anywhere else. They identify 3 - 5 or so players they really want to go after and then see if there's anyway they can make it happen. Last year, there were apparently three guys the Jazz really liked. One was Mitchell. One was probably Markkanen (just guessing), and then there was a third guy--maybe Jackson or Tatum. They then went through the process of figuring out how they could get one of those guys, and they worked out a deal with Denver. (I don't believe the deal involving #24 and Trey Lyles was last-minute. It was a contingency they worked out days if not a week or two in advance. It then moved forward when the Paul George-to-Cleveland deal fell through.)
In other words, the Jazz try to use the draft to maximize their ability to bring in young talent and they target someone specific they really believe in. Usually the players they want in the draft are at or above where they are drafting. This year, for example, I'm guessing they really like Doncic, Bagley, Jackson Jr., Mikal Bridges, Miles Bridges, and they'll make attempts to make a move to get one of them--though, unlike last year, they don't have a young prospect they can trade to move up.
There are also a few guys that the Jazz really like who might realistically be available at #21. Just guessing, but those players probably include Walker, Zhaire Smith, Huerter, KBD, Brown, and maybe Okobo. They might also have some interest in Melvin Frazier or Okogie (again just a guess). They probably won't pull the trigger on a deal to move back in the draft unless: a) a guy they're targeting at #21 is no longer on the board, b) they really like guys further back in the draft, and c) the value being offered to move back is compelling. They might have a contingency in place, but that deal wouldn't be made until right before they pick.
If the Jazz decide they freaking love Jerome Robinson or Josh Okogie, if they feel safe moving back to #27 to get one of those players, and they like the value being offered to swap their #21 pick, then they may do it, but not a moment sooner.
A couple years ago, the Jazz had targeted the Bolomboy kid from Weber State as a guy they liked in the mid-late 2nd round. Other guys they wanted to draft were gone by the time their 2nd-round pick came up. They were confident Bolomboy would be there at #52, and they traded back several spots in the 2nd round for $3 million.
That's how the decision-making process works, imo.
