Quote Originally Posted by Scrap Irony View Post

Middle reliever Josh Hancock died.
Ace pitcher Chris Carpenter was on the DL all year (relatively) and had TJ surgery.
Yadier Molina was put on the DL in May with a broken hand.
Jim Edmonds, Tyler Johnson, and David Eckstein went on the DL in June. So did Braden Looper.
Scott Rolen and Scott Speizio ended their seasons in August.

That season, Brandon Ryan, Adam Wainwright, and Chris Duncan were all youngsters pressed into larger roles that thrived. Ryan was a rookie; Wainwright became a starter, and Duncan was a second-year guy.

The Cardinals also lost four starting pitches to free agency from the year before.

No team could withstand that amount of injuries.
I think this is the biggest reason here. There was no way they could lose four starting pitchers and be competitive.