Otherwise all those crashed Star Destroyers and Super Star Destroyers would have obliterated all life on the planets they crashed into (if not the world itself). Yet they didn't even make so much as a notable crater. It also helps explain why their antigrav technology is so powerful and reliable.
I didn't get the impression those Star Destroyers had crashed. If they had they shouldn't be as intact as they are. It would have to have been a controlled landing. If it had been an actual crash, not only would there be the huge crater you speak of, the Destroyers themselves would only be debris scattered all over the desert.
I've no idea what happens in Battlefront or how canon it is but the impression I got was the imperial fleet was scuttled shortly after the Battle of Endor.