I frequently fly PHL-LAX-LAS. The PHL-LAX flight I take is 726, leaving around 3:45 give or take ten minutes, and it's been a fixture on the schedule for at least two years. It arrives in LAX around 6:45 (again give or take 15 minutes) and there are various connections - these do change.

On July 4 and 5 however, I can't seem to book this. I've checked AA, ITA, and Orbitz. 726 is operating, and there are connections in LAX. The individual flights are available, but not as a single routing.

What could be going on? They are available other days.