Perhaps they knew the design was flawed, or perhaps they made a very foolish decision (since they would have profited handsomely if the design could be fixed).
It's not like these decisions are being made purely on a scientific basis.
In reality the FDA is too conservative due to the incentive structure: people getting hurt from a drug approved too fast are very visible. People that get hurt due to a drug being approved too slowly are not. This is the core issue.