The Jones are in different territory with Dak right now. McCarthy got a good look at Dak, we don't know what he thinks about him. Also, we are having a terrible season and have lots of holes. I'm sure Jerruh and Stephen never thought they would have a shot at the number 1 or 2 pick, and could grab Lawrence or Fields possibly.
If they draft Fields, and move on from Dak, they save 40 million, and can spend that money all over the defense and O-line. Plus will have high draft picks every round to fill holes. They won't get this opportunity again.