Banks don't win IPO mandates by quoting the board of directors a valuation that's lower than the last round.

Both Goldman and Morgan Stanley gave the BoD much higher valuation numbers, which made members believe the stock price was going to go up... and when your options are going up in price, it's easiest not to rock the boat, and ignore misdeeds or conflicts.

You only realize who has been swimming in the ocean without trunks when the tide goes out ;)