Weather delays and cancellation are always an issue, especially this time of year.
There have been a few airlines that have also experienced staffing issues. JetBlue Airways and Spirit Airlines had issues last weekend because of that. JetBlue plans to proactively cut flights for the rest of April and it also expects to reduce its summer flight schedule by at least 8% to 10%.
Alaska Airlines has sited training delays causing flight cancelations.
This is not just a US based problem. British Airways and Easy Jet have been canceling flights due to staffing shortages caused by a soaring number of coronavirus cases.
Of course, a lack of flights also means a lack of a backup plan if things do go wrong. If the 2:00 PM flight on Jet Blue is cancelled, that is one thing. But if American Airlines got rid of the the 4:00 flight, well, there is not enough excess room to move people around.