They probably think Ryan fits into the long-range plans. e.g. beyond this season. The fan base thinks of tomorrow, the front office has a three-year vision. Ryan has more value to the Cardinals than to another team. He's done less than nothing in the league, but he provides depth for the Cardinals.
B.A. wasn't here, but Steve Keim was in house when the Cardinals dealt away Tim Hightower, then watched Williams and Beanie get hurt.
The good teams are at least four-deep at running back for a reason. [see the Niners and Saints]