Is there a point in posting the same old material over and over ?!
Just saying...
There are a few things going on with that
1) The more enthusiasm there is about a model the more reposts her thread is likely to have.
2) It used to be that many members would take the time to scroll back and check several prior posts in order to avoid making a repost. Nowadays not so much.
3) A certain number of reposts occur because the same galleries are hosted by so many different sites. On the other hand, most of those reposts could be avoided by using the method in 2) above.
4) Some galleries from the same set have a slightly different mix of pictures, which can be a good thing.
5) Some posters are interested in padding their post counts and therefore could care less about making reposts.