Why did the religious 'conveniently' lose the ark of the covenant and the stone tablets?

One has to wonder. If the Ark existed or if the stone tablets with the big 10Cs existed, then the religious might have some tangible, credible, irrefutable evidence of humanity having been in contact with a 'god'. Of course, no one ever seems to get their hands on a piece of a flying saucer, either. Does that make 'god' and 'flying saucers' equally credible?