A recent effort to clean up a northern California canyon overlook site has resulted in the recovery of more than 50 vehicles. Some were simply rolled down embankments, others were quite obviously launched at high speed by drivers looking for a shortcut to the start of the reincarnation line.
This sort of thing would seem to be rather common. I remember reading years ago about a murder investigation involving the search for a woman thought to have been murdered, whose body was stuffed into the trunk of a car which was then rolled off an embankment into a nearby river. A search of the area didn't find that vehicle, but it did find some dozen or more others which had been... disposed of... for many other reasons.
People will just toss any damned thing in a river, it would seem.