Airlines have an incentive to blame factors beyond their control for delays. If the cause is weather, air traffic control, or a similar issue they’re going to owe customers a lot less (if anything at all) compared to when a delay is ‘controllable’ or their fault — such as when a flight goes mechanical or when crew simply don’t show up. (EU rules are somewhat stricter.)
Customers can be sitting at their home airport and will get frustrated when they’re delayed by weather only to look out the window at blue skies, knowing weather is clear at their destination.