Holding on to the depth
The Cardinals did a good job dealing expiring contracts. Jack Flaherty, Jordan Montgomery, Chris Stratton, and Jordan Hicks were all set to be free agents at the end of the season. In a lost season, it made tremendous sense to get as good of a return for these players as possible. Paul DeJong was in a bit of a unique situation, as his contract has some opt-outs in the upcoming years.
In addition to the players who were traded, the front office should have traded from its depth. Dylan Carlson, Lars Nootbaar, Jordan Walker, Tyler O'Neill, Alec Burleson, and Tommy Edman can all play the outfield; Brendan Donovan (now out for the season), Tommy Edman, Nolan Gorman, Taylor Motter, and Jose Fermin can all play in the middle infield. DeJong's departure and Donovan's injury clear up the infield logjam slightly; however, there are still plenty of players who could have been traded.
Dealing Nootbaar, Edman, Carlson, Burleson, or Gorman would have netted a supreme starter for the rotation both this year and next year. I'm sure talks were had, but the prices were too high for a player of Logan Gilbert's or Dylan Cease's caliber. It still would have been nice to flip one of these controllable players from a position of strength to a team that could help an area of weakness for the Cardinals.
While it will be difficult to see long-time Cardinals such as Carlson, Edman, or O'Neill be traded this offseason, hopefully, the Cardinals can get a controllable, high-end starter in return. Depth is usually a good thing unless there is a serious dearth in another department.