Whether it's actually a good idea isn't something I know enough of the real numbers to comment on, but it seems plenty possible that an expensive step that substantially reduces risk might be appropriate in some circumstances and not in others.

> if the regulatory process is truly about safety why does this exception even exist?

Because the risk is worthwhile at times.

The exceptions typically apply to rare diseases that impact a population too small to be profitable enough to justify the $1B or more it may cost to shepherd a device or medication through the normal process.

These are populations who would be potentially unserved otherwise. (I'm of the personal opinion that this is where the government should step in instead of private industry, but I'm pretty left of center.)

https://www.fda.gov/industry/developing-products-rare-diseas...

IIRC, an exception of this sort was used to expedite an Ebola vaccine due to the recent outbreak... because, well, Ebola.