That article offers good arguments not to pick him. Add to the fact a former starter is going to demand a greater salary, and his weaknesses will be more well known than, say, a rookie or someone who's always been a backup. At this point Colin has peaked and declined, and everyone knows it.

Edit - backups should be technically solid and be able to execute the same plays as the starter. Not flashy and unorthodox. When your starter is injured you don't want the whole team to have to change systems.