I think the problem came in recently when the SEC and Big10 started talking.
Initially you were hearing rumors that if FSU and Clemson could get out, that opens the doors for others like UNC and Miami and that might result in ND having to look for another solution if the ACC fell apart.
Then all of a sudden, those rumors went dead.... Then right after, you hear that Big10 and SEC are chatting it up.
I believe the Big Ten just said, why rush this.... if at all... nothing assures that these ACC teams will be available. By doing a scheduling alliance, they pretty much add another 4-6 premium games per year... vs adding lets say UNC and a FL team -- making sure that they bring enough value to increase the pie.
Why not just the 10th game between the 2 conferences as an OOC... 4-6 premium games plus another 10 that people from both conferences will watch just to see the who wins.
At this point, if the B10 and SEC still want an ACC team........ they don't mind waiting until 2036. And without the Sure Thing in the P2, i don't think any ACC team will be paying to get out early.