Everyone knows Colorado (and others) are talking to the BIG12 while waiting for details of a potential PAC TV+GOR deal. That's blatantly obvious.

Your question, as I see it, is more about the RISK FACTOR. In other words the BIG 12 may possibly have multiple options for adding schools in the near future (e.g. IF a sudden ACC breakup? Or the PAC does not get an acceptable TV deal? Or PAC has GOR issues or uneven distribution issues? Or OR/WU bolt? etc -all of which are at least possibilities). So if Colorado (or some other team) is told —matter of factly— that they are CURRENTLY the BIG12's PREFERRED and REALISTIC expansion candidate, but that that could change if circumstances change; then Colorado (or other invitees) is/are running a HUGE risk by not accepting the bird in the hand. There is a real possibility that some schools will be left behind, essentially relegated.

So the question is a good one: why would CO+ not be first to accept the bird in the hand? The only answer I can think of is they have information that convinces them that the PAC10 (i.e. including OR/WU) still has a good chance of survival. The other possibility is that the BIG12 itself is NOT extending a committed offer, because IT is also stalling, i.e. playing the waiting game.