If you ever see an infrared movie of one of these evacuations you'll see how contrived the whole situation is. First, take a bunch of Highly Motivated, young, athletic flight attendants. Dress them in running shoes and shorts. Clear all obstacles (no reclined seats, or tray tables, or blankets, or laptop computers, or fat old blind people allowed. Then rehearse a few times to get the sequencing of the moves right.

Then, on a signal, the athletic young weightlifter at the window quickly takes out the door and throws it away, while the participants literally RUN down the aisle and jump unhesitantly into the chute or onto the wing.

It is a total fiction, and it is not surprizing that there were a few injuries.