Choosing not to address starting pitching
I'm sure by now most of you have seen the meme or remember John Mozeliak's quote from this offseason that the team has "six starting pitchers" when asked about a potential pursuit of pitching help.
The Cardinals were never going to be in the Jacob DeGrom, Justin Verlander, or even Carlos Rodon market. And in hindsight, none of those guys would have made a major impact this year due to various injuries and underperformance.
Where the Cardinals did mess up though, which our own Thomas Gauvain broke down in depth last week, was not pursuing some of the "mid-tier" starting pitchers with high upside this offseason. Nathan Eovaldi, Zach Eflin, or even Chris Bassitt would have provided the club which much-needed stability in their rotation and would have come at an affordable price.
While I don't blame Mozeliak for not seeing the rotation being this bad this year, not bringing in an outside arm was a big mistake.