Computers, like me, are lazy and do as little as they can get away with.
When you delete something from your wastebasket, the computer simply notes that the hard disc space occupied by the item can be overwritten when more storage is needed (and Windows cannot find the item).
Similarly when you re-format a dive (not low level), the computer only writes what it needs to.
This is why whenever disposing of your old PC you should remove the hard drive and smash it to a pulp (otherwise Nigerian scammers may get hold of your bank details).
I have recovered information from a hard drive that died and had to be re-formatted before the PC would recognise it to be present.