Unfortunately there are numerous reasons why people turn up late ranging from being plain bog stupid to the anus' who think they are more important than the rest of us. But you get these types anywhere. Just look at the line in your local supermarket for examples.
The problem lies where they have checked in baggage that has to be found and off loaded. This is pure bag lotto so the time needed can vary from 1 minute, to 20 minutes where Murphies Law kicks in and the bag is the last one pulled out of the hold.
Just another day, another d*ckhead.