Most of those guys weren't exactly household names, though. I think the larger point is that coaches like Jason Garrett and Gary Kubiak were once role players or back-ups, you don't often see the likes of John Elway or Joe Montana go into coaching.
However, players who've become coaches and/or coordinators is quite long. This list doesn't even include the coordinators who were once players. Guys like Emmitt Thomas (who actually is a Hall of Famer), Ray Hamilton, Mike Mullarkey, Russ Grimm, Chris Miller, Bryan Cox, Al Harris, Tom Rathman, Henry Ellard, Matt Cavanaugh. Also, remember that Hall of Famers Bart Starr, Forrest Gregg and Mike Ditka were head coaches, and hall of famer Joe Greene was a long-time DL coach.