Even leaving satellite images out, I don't understand either how this only got discovered now. Is China so sparsely populated in some areas? I understand that n

Even leaving satellite images out, I don't understand either how this only got discovered now. Is China so sparsely populated in some areas? I understand that not every place is like Europe where every square centimeter has been utilized by humans in some capacity throughout history, but even in comparatively empty US, I cannot imagine something huge like this only getting discovered now. Mexico has lots of sinkholes and there have been massive efforts to fully explore those, including autonomous submarines for mapping. Yet here is an enormous sinkhole in a country of 1 billion+ people and it gets "discovered"