We know that there will have to be tough roster decisions with this team in the near future. Is the plan to put those off until the offseason no matter what? If that's the plan, you might see a rationale for keeping the status quo. At the same time, I'd be fine with making one or two of those decisions by the deadline.
But let's be honest here, you're talking about the risk with one player (Norby) by making the change I'm saying to make. It's not going to derail the future of this team or even his trade value.
At the same time, I think they're doing Holliday a disservice. He only played 36 games in AA, and half that in AAA, last year. They didn't even give those leagues the chance to adjust to him. I really, honestly, think they've rushed the kid. I think he's showing that he's not ready offensively, or even defensively at 2B. Heck, I think he's overhyped in general even though I definitely see him eventually as an above average 2B and top of the league leadoff hitter. But he's not the uber athlete, big powerful MOO bat that someone like a Gunnar is. He's more of Jeter profile. That's wonderful, but it's not an ARod profile either and Jeter did what he did with 10/10 intangibles.
I think there's more to gain by getting the extra year of service time and making sure he's ready, and I think that way outweighs the risks of losing some value on a guy like Norby.