Obstacle one
Depth belonged to institutions.
An ordinary person’s telling could not be carried far enough to be worth keeping. Following a question properly took a library, a laboratory, a supervisor, years. That apparatus belonged to universities, and to the people universities admitted.
So the tellings that survived were the ones with resources behind them. Natural history was open to self-taught people until professionalisation, in the late nineteenth century, recast their work as anecdotal and closed the door.
Everyone else’s telling was simply lost — not refuted, not judged, just never carried far enough to be written down.