Why Tutankhamun escaped discovery previously

Tutankhamun was king at a time when pharaohs were no longer buried in pyramids or other above-ground monuments. His tomb was typically underground, carefully hidden and placed where no-one was likely to find it; the entrance was sealed and the steps down to it concealed beneath rubble and sand. From the surface no trace of it could be seen, so unless a person were deliberately looking for such a tomb it would be impossible to find.