It become a trope for a reason, our ancestors did manage to lose some pretty useful knowledge sometimes. I mean, by now we have managed to figure most of it back out in the current modern age but for awhile it was lost and that is where the trope came from. And if nothing else looking back over their work might give people ideas on how to take some old ideas and run with them in new ways like how people looked into leeches and realized you could make an anticoagulant out of things in their spit that is useful in cases were patients are allergic to more commonly used blood clot fighting medicine....