IMO, the problem resides more with user perception.
Even if every user knew how to get rid of such files, and knew how to do so in a thorough and complete fashion, they still might not bother with even a single click disk wiper... they tend to think nobody would bother with such efforts as these people put forth.
Corporate 'Information Technology' people are the same way - some have have handed me older drives which still booted, I was the one who had to erase them!