This has never been stated and is just my assumption, but I'm guessing since Women seems to be expanding in terms of number of girls and influence in the industry, it is a way to maintain a boutique like feeling, Supreme board, Women board, Women-direct board. Instead of being a behemoth like IMG where there are SoooOooo many girls on their development page alone.
Again.. just my assumption/guess.
On a side note, does anyone know why girls are with Women Worldwide, but are not listed on Women NY's site? They appear in Women Milan very very fast, but Women NY takes very long to add girls, and seems more selective who they display.