I think
WOTC was happy with the
OGL as long as they could say
"See? We no longer have to publish adventures and we get people purchasing our PHB"
It is things like True20, the pocket PHB and Conan that soured
WOTC I think. Here where products that used their work yet at the same time, DIDN"T force consumers to have the
WOTC product.
As time went on, I suspect since the latter was the more common approach, many at
WOTC were wondering, "Um, how does the
OGL actually help us again?"