I think enacting it early would just make it look like a Democratic party alliance. That's roughly who the enacted states are currently and it would dissuade other states who might benefit or believe in the popular vote from joining.
Right now, it's in the abstract interest of Texas to join the Compact, because a popular vote would increase their influence, but if the Compact involved just being forced to vote blue indefinitely without gaining any influence, then it's a bad deal. "Doing what the majority of the people" want is a lot easier a concept to sell than "doing what the majority of blue states want".