“Isn’t a biological reason for this to happen.”?
How about self preservation.
For simplicity, say you drowned and get cpr. If your brain doesn’t try to restart, cpr wouldn’t work.
It’s a good assumption that brain activity after death is related to the body trying to live. That trait would be evolutionarily advantageous enough to be ubiquitous. Getting one last trip down memory lane is not an evolutionary advantage, it’s a side effect.