Ghosts must remain close to the place where they died. Dinosaur fossils are underground, therefore dinosaur ghosts are as well.

Since you don't follow your remains after death (people ghosts tend to haunt houses rather than graveyards) it means we have no method to excavate them. They will always be underground.

This is the fate of all ghosts, to slowly be buried by time until you wander the dark abyss alone.