Classic "alleyway congestion" in LAX. DL and AA are both particularly constrained by it. AA is especially challenging right now due to the TBIT construction on the west side of their terminal.

IME, this is always worse for DL at night around the 9-11pm push which involves many red-eyes + SYD departure combined with tons of arrivals. The alley, as it were, gets extremely congested during those hours. Be grateful you didn't end up at one of the remote gates at the west end of the airport, AA has been forced to use those recently due to construction (and the buildup of their LAX network). Real PITA in the evening.

UA is a bit more isolated on its own toward the far end of the airport. Not sure if alleyway congestion affects VX/T3. I was flying WN fairly frequently and the evenings could be hard for them as well. Then again they do not have many outbound ops at that hour.