An evacuation is a serious business which often results in injuries in itself.
It is all very well second guessing the crew but any decent crew will make decisions based on the best information they have at the time.
For example what about the QANTAS B747 which slid of the end into soft ground at BKK some years ago. I don't believe any evacuation was ordered there despite partial gear collapse.
Thankfully I have never been in any situation requiring a decision to evacuate/no evacuate but as is so often the case it is not the obvious problems like a visible fire but the less clear cut problem which makes the decision fraught with difficulty for the crew.