Some of these models move on to other ways of making a living . They quit modeling and have thier images and profiles removed, this is one possibility.
Thee are server errors that occur and leave files missing or deleted as well.
MUCH of the file database from the INDEXXX was lost in exactly that way.
If you'll notice - files that are form before about 2010 are no longer in the listings.
This model is from 2005.