[alatar]

I would say that there are two reasons for leaving Orcrist, "Biter," where it lay. First, as many peoples and races honored their dead by burying them with the dead's possessions and beloved artifacts, like Thorin with his sword and the Arkenstone, one doesn't then wait a while to take the objects back from the dead. Also, my guess is that these magical and great items have to be 'lost,' or there would be nothing fun to look for in later ages (plus you don't want a First Age weapon on the streets during the Fifth Age...).

I cannot see Dain or his folk to be so desperate as to desecrate the tomb of their 'father' just for the use of a sword.

Welcome to the Downs.