One factor is that this is not in the same river system as the 29 already discovered large sinkholes in the area. This is from something called the Fugui under

One factor is that this is not in the same river system as the 29 already discovered large sinkholes in the area. This is from something called the Fugui underground river / water system. I'd guess that it had been discovered before though. Perhaps just not explored in detail, by a caving/karst research group.