Why do some theories speculate that the capacity of flashbulb memories is an adaptive characteristic?

A given trait is adaptive if it helps us (or helped our
ancestors) adapt to their environments and have a better chance of living long enough to
pass on their genes.  Therefore, what you are asking is why people who had flashbulb
memories would have a better chance of survival than those who did
not.

As you know, flashbulb memories are long-lasting and
are triggered by intense emotional events.  This sort of capacity could be adaptive
because many flashbulb memories might have been triggered by life-threatening
experiences.  Such experiences would surely trigger very strong emotions and, thereby,
flashbulb memories.

Imagine the difference between a person
with such memories and one without.  The person with such memories would remember what
sorts of situations almost got him or her killed and would avoid them.  The person
without such memories might forget these lethal situations and blunder into them again
and again.  This second person would be much more likely, over time, to get
killed.

It is in this way that such memories could have
been an adaptive characteristic as the human mind was evolving.