At a random guess, I'd say partly to stop mass hysteria and panic, where these sightings occur?
AND, also the fact that the gvnmt wouldn't have to pay out, if no evidence/bodies of big cats couldn't be proven, as in when someone reports a big cat body at a certain location, when they go back to check, lo and behold, the body has 'miraculously' disappeared?!!
Just a guess, though. I might be way off the mark?