Discovered? I had the pleasure of talking with some Mayans and they have portions of the jungle cordoned off because they dont want the ruins disturbed, its a big part of their spiritual practice, the pyramids are essentially tombs erected on top of where a person died. Even mentioned to me that tourist roads are bad according to the culture, but they build extra shrines to appease the families of the dead, and assume the spirits would not like to see their relatives living in poverty, so they allow heavily sanctioned tourism there. Its likely the local Mayans even know whose families lived in this place.