Exactly.
Timber cruisers, oil hunters, precious metal prospectors, US Geo Surveyors, Forestry people, etc would have stumbled on something by now.
If they bury their dead, why don't they make stone or wood tools? Or leave behind some crude shelters? Or simply occupy caves which would protect much evidence like feces, hair, and skeletons? There would have to be a breeding population, so they could not be so rare and scattered. Where are the young, stupid juveniles that wander onto roads? Where are the fossil remains?
If Bigfoot existed, the greys would have abducted and probed one by now, and they have not mentioned that to me.