Mainly because it's not been updated to include the 10 new scholars who signed on in summer (Aarran Racine, Callum McNish, Sam Argent, Ryan Tafazolli, Lewis Page, Ben Reeves, Garyn Preen, Tom Dunford, Tony Garrod and Daryl McLean). In addition, Jeffrey Imudia and Mikael Dolinajec are also missing.
However, it seems the OS are working on it. If you click on one of the players and go to their profile then amend the ID number at the end to 163 (or above) you get incomplete profiles (no photos) of most of the above (but not Page and not Imudia). For example, here is Aarran Racine's profile (which shows he's been given the number 38 shirt).
http://www.saintsfc.co.uk/team/?page_id=6587&player_id=165
I see that Poke and Saga have both been removed - unlike last season when loaned out players were still listed.