Everything went downhill because of "muh covid."
Whether they want to admit it or not, I believe they never expected travel to pick up as much as it has and as early as it has -- even on the earlier days of the initial recovery from the pandemic. Hiring decisions, scheduling etc were probably based on those underestimated assumptions.
It's probably also why there are still sad boxes.
Delta not only ceded all of its advantages it had pre-pandemic but now seems to be underperforming in those metrics. Really disappointing.
All of this while SkyMiles got gutted and service cuts were made in premium cabins, SkyClubs got insanely crowded, DL One lounges 10+ years too late, and old planes keep flying internationally