Why does not have "Wipe Free Space" for all Drives?
Two things
1) It does, under options>Settings you can check off any drive that is PHYSICALLY attached to the computer (no network drives)
2) Wipe Free Space really ought not be run unless you are selling the drive, multiple uses will reduce the life of your drive as it performs a large amount of writing. This is ESPECIALLY true of flash based memory as the chip can only perform a finite number of writes in it's lifetime, but any hard drive will also wear out from WFS