Earlier quoted context omitted.
> while any primitive civilization will quickly figure out "hey this place is definitely cursed; we shouldn't stick around". After a while, when quite a few people have died, and maybe their whole village and all their farmland is contaminated. This is exactly what we are trying to avoid. See for example the Goiânia accident: https://en.wikipedia.org/wiki/Goi%C3%A2nia_accident
By that example, it sounds like "after a while" would be "a couple weeks". That's a short enough timeframe to piece together "oh darn, this happened because we went into that scary place with all the jagged rocks and took the curse of that strange land back with us". Maybe that particular village is doomed, but villages do communicate/trade with other villages and could spread the word that "hey, we visited this weir…
And in the linked example it was highly radioactive, and people fell sick and died within days. More likely is higher rate of cancers, stillborns and different kinds of genetic damages. How long is it going to take before people connect those things to the strange mines?