I think with so many Chimps, they must have many smaller groupings and even the functional 'cages' are designed to hold all of those. I imagine the forested Islands are a newer development and the cage enclosures were there first. The biggest groups they can get together will be the ones that have access to the forested areas I imagine. But its a huge improvement for all 200 of them. I imagine all the ones that still can't access the large islands live in a good and satisfactory environment compared to what they once endured.