There are two kinds of errors an FDA type agency can make:
A: Approve a drug that turns out to be a "cure worse than the disease", and shouldn't have been approved.
B: Not approve a drug that would have cured many sick and/or saved a lot of lives.
You can never fully know beforehand which error a decision will have. So the FDA will always gamble a bit in their decisions.
And here is the gigantic problem:
With a type A error, patients taking the new drug dies, there is an uproar in the media, the agency takes a big beating, and careers are ruined.
With a type B error, a lot of people who could have been saved dies. But that is no change from before, no one notices, and the careers of FDA officials are unharmed.
Given these incentives, it is not surprising that the FDA overwhelmingly errs on the side of type B errors. It's hard to compute, but the number of lost lives from this is probably in the millions since the 60s.