Poor management
Here is one that I just think it is more complicated than we'd like it to be. I'm not saying that Oli Marmol is the right guy, and I'm not saying he's not a big reason why they've struggled, but I'm also not sure getting rid of him fixes things. Still, it's clear that there have been managing errors all season.
It's easy to point to weird bullpen decisions when a team is struggling, or question lineup construction each day, but where things have really seemed to have emerged is in the public treatment of players like Willson Contreras, Tyler O'Neill, and Jordan Walker.
Quick caveot, it's hard to know how many of those decisions (outside of the O'Neill one) were from Marmol or from the front office. But still, he plays a major role either way.
It feels like an eternity ago that O'Neill and Marmol were at odds about his "hustle" in a game against the Atlanta Braves back in April. The Cardinals' relationship with O'Neill has seemed strained for a while, but this seems to have been the nail in the coffin. The Willson Contreras removal from catching duties and then brought back to them a week later caused major stirs, both locally and nationally. Sending Jordan Walker down, although it seems to have paid off, notably impacted him and caused many to question what the Cardinals were doing having him on the roster in the first place.
Marmol has got to answer for those, for his questionable decisions in game at times, and ultimately, for the performance on the field.
How can a team that was supposed to be as good as the Cardinals were, underachieve like they have, and not have any managerial issues? Maybe it was one of those player situations, maybe it was a lack of clubhouse cohesion back in the Spring, or maybe it was something else. But at some point, Marmol has to be held accountable, just like this front office will too.