I expect there are a dozen equally possible to occur catastrophic failures that the team at NASA knows about, has analyzed, and the decision has been made to take the risk and launch.

Spaceflight is complicated. We don't know everything. There is a lot of unknowns that happen everytime you light off a rocket.

It is a lot easier for Elon, as the loss is only a pile of money.

Without ever working at NASA, I expect there is a week long "risk management prior to launch" meeting where many, many issues are brought up, discussed, and decided.