OK, this is a rush job, and this work may already exist. Please feel free to pitch in.
We don’t learn from other people’s mistakes because
– the pain of making a mistake is absent
– we don’t (want to) recognise that “there but for the grace of gaia go I/we”
– we are better than those losers who made such an obvious mistake.
We don’t learn from our own mistakes because
– we choose to ignore painful things
– we never make mistakes (it was unavoidable circumstances etc etc)
– we’re too busy finding a scapegoat
And if I had to boil it down to a single word – ego.