Skating is not easy to improve when you've been playing hockey for your entire life. There is so much ingrained muscle memory that any improvements you can make as a 20-something are marginal at best, and as you're approaching the elite level of skating needed to hack it just as a depth player in the NHL, making those marginal improvements gets harder and harder.
Skating is core to the game and the league is the fastest its ever been. It's a fundamental skill for which there's no quick or easy fix. I'm always very dubious of prospects with skating issues. We're not in a league where slow but smart players can make a long career trailing the play and setting up on the wall to make some passes anymore. For a long time, that was a viable route to NHL success- see guys like Cory Stillman. But it's not anymore, and those guys become AHL lifers or leave for Europe instead.
Anyway, this deal gives Carrick a real shot at the NHL, which he deserves and I think he can handle as a bottom pairing guy, and leaves the Checkers with a solid AHL defender who they likely don't expect to be anything else.