Well duh, it's obviously because they didn't win enough games.
There's plenty of reasons for this, the offence and starting staff was s*** in the early going and the team was largely kept afloat by a stellar performance by the pen. The pen started to suffer from injuries and tanked soon afterwards as the remaining dependable options were overworked. The sudden in season sticky stuff ban made the club's primary setup man completely ineffective from that point forward. It would have been nice to see some help brought in a little sooner, but aside from massively overpaying it didn't seem like there were trades to be made early in June or so when the pen became an issue.
There's also the not so insignificant fact that for the first 4 months of the season the team basically played as the road team in their "home" games and faced hostile crowds, while also facing the prospect of moving in season several times. This team faced far more adversity than any other team due to the covid pandemic. It's unfortunate that they missed the post season by a single game, but given that they played in a murder's row division where there were 4 teams that won over 90 games I'll give the GM a bit of a pass.