Because of the GNU Public License he slapped on there. Matt was free to change the licensing model at any time in Wordpress’s history, so it’s really quite befuddling when people like these contributors encounter a bait and switch, that apparently forking a GPL’d project is against some terms of service.
EDIT: was Wordpress GPL’d all along because it’s a fork of b2/cafelog?
EDIT: was Wordpress GPL’d all along because it’s a fork of b2/cafelog?