At first I was surprised they didn't use the emergency slides, but I suppose once the aircraft is on the ground and there's no evidence of a fire or similar, it's safe so there's no immediate need to deplane the passengers.
Ftom all the videos of planes I've seen, I think slides are deployed only when fire is involved. Since the damaged engine didn't start any fire for 2 hours, the pilots probabaly knew there was no need to deploy the slides when they landed.
The risk of minor injury (sprains, etc.) is pretty high for slides and there is some risk of serious injury (broken bones and worse). They are used when the alternative risk is death.
It doesn't seem fair to use the rate of injury during an emergency evacuation as a measure of what could be achieved with the same slides under non-emergency conditions.
The height is the same, and that's where those injuries come from. Those slides aren't like playground slides at all --- they are very, very high, and especially so on an A380.
Also, they need to be replaced if used, which costs extra time and money.
