How Wells Fargo Exemplifies the Drivers of Big Corporate Fraud:

You should read the whole thing, but here are the bullet points from the article:

1. American businesses have become stock manipulation machinesAmerican businesses have become stock manipulation machines
2. Focusing on short-term stock prices leads to corruption 
3. Punishment means little until executive pay is understood

Go read the rest, and pay particular attention to the SEC under the Reagan administration legalizing stock buybacks in 1982.  Prior to that they were considered illegal stock manipulation.