Perhaps some of the delays are caused by higher loads?? If they have a light load < 50%, they can board and exit (and get bags on and off) much faster and make up time. But recently I have rarely been on a flight less than 80% loads - and when it is at or near 100% load - the loading time and unloading are much longer due to overhead searches, baggage, looking for seats, people moving to accomodate couples and kids, etc.

And I notice that it used to be WN "pushed" people to board and get seated quickly. More casual now.