The Utah Jazz weren't wrong to think that John Collins may not be a good fit on the team. During the first 20+ games of the season, the only two players doing worse on the court than Collins were Jordan Clarkson and Keyonte George. The team was bad, and they were bad in part due to their collective play.
But as the season has gone on, the three of them, namely Collins, have started to look better. He's not playing up to what was hoped in the offseason, as many thought he'd have the same kind of year that Lauri Markkanen had last season, but he's better in January than he was in December.
So when the Jazz first put him on the trade block, it made all sorts of sense. He was out of position a lot, defensively he seemed to be lost and he just wasn't making an impact. His play has gotten better, but again, it's not like he's taken a step into All-Star potential, but he is better in the system now. Making the news that the Jazz are no longer actively looking to trade him makes sense.
The addition of Kris Dunn and Collin Sexton to the starting lineup has greatly improved the team, with far fewer turnovers, better passing, better shot selection, and better defense. Though we can't deny that Simone Fontecchio as a three-and-D wing didn't help the defense some either, because it did.
The Jazz are significantly better right now than they were just two months ago, and they're tearing their way through playoff team after playoff team, with a team as hot as the Jazz is right now, you don't mess with the chemistry. If there's a no-brainer trade, a Luka Doncic-type of trade, you still make it. But you don't trade an impact player for, what will likely be, three late-first-round picks over the next six years.
Since Collins is once again a positive asset and you're streaking to a winning season, you don't make any major moves. It's just common sense.