I agree that Penn Station, New York is a tough place to operate from, due to the vast amount of train and pedestrian traffic, in an antiquated infrastructure, that was made even worse, when they built the 'Garden' above it, and added the additional support columns to support it...right when traffic started growing fast in the station. Hopefully, the expansion into the old GPO will alleviate a lot of that in the future. As it is now, the platforms, with the exception of one extra wide one used by the LIRR, which doesn't really need it, are extremely narrow. They have very little room between the platform edges and stairways, elevator's, support column's, etc. Add to that mix, commissary carts, baggage trucks, baggage, wheelchairs, crowd's...it just wasn't designed to handle what it is handling today. To fill a platform with a large crowd, with other trains entering or leaving could result in a disaster. So it is best to keep passenger's off the platform's until the train is fully ready to board, and the platform is clear of obstruction's or detraining passenger's.
That said, I agree that when boarding is ready, they should (and IIRC sometimes do), announce "use all stairways down" to the designated track.
That said, I agree that when boarding is ready, they should (and IIRC sometimes do), announce "use all stairways down" to the designated track.