If you evacuate a full 747 using the slides, the chances are you will probably kill someone. Therefore you factor that into your decision making and I suspect in this case it it was considered safer for the passengers to remain on board. Had there been a fire, I would suggest the decision may have been different - but there wasn't. The option remained throughout but I consider the right decision to have been made.
Disembarking via steps away from the terminal is not the easiest thing to arrange either so there's another reason why passengers remained on board for a while.
I note that no-one was injured and I wonder why it is considered by some that escalating a situation from undesirable to hazardous-to-life is a sensible course of action?
