I would say its because those "mistakes" are profitable to some who are in a position to ensure nothing shatters the illusion of intelligence with which we are endowed.
Because of temptation.
because we're stubborn and perhaps decide to face the consequences afterwards
Because our basic motivation...greed...hasn't changed at all.
mistake is a judgment after the event .... very few events are under control some of them just happen ... you can watch try but difficult . simply saying the judgement on the victor of a war is almost always fair .
It's more comfortable to point out the mistakes of others and pretend we're "cool". Also, I think, as a whole, people live their lives more in busy and reactive mode, rather than reflectively, which is key to learning from our mistakes. Then there's humility, which helps in learning from our mistakes, but is in short supply in a society where people are compelled to "sell yourselves" and have self esteem.