Why didn't the Pac 10 do that?
The Pac-10 expanded at a very turbulent moment when it looked like the Big XII's walls were crashing down. They were trying to make a play to create the most powerful conference in NCAA. Everyone thought the ground was radically shifting, but Texas halted the drastic shift by holding the B12 hostage as 10-team league. Time was of the essence, so the Pac had to move quickly.
Or the MWC for that matter?
The MWC has been engaged in all-out war with the WAC since realignment started last summer. Every move has been defensive. When Utah-Pac rumors built, MWC snagged Boise to try and keep hope of attaining AQ status. When BYU was ready to bail, the MWC took Fresno & Nevada to hold the league together and prevent the WAC from carrying any weight in the west. The Hawaii addition is either (1) preempting TCU's departure, or (2) a shot at the WAC's corpse and attempt to accumulate the most known non-AQ teams west of the Mississippi.
The Big East isn't in a hurry to hold their conference together or to make defensive acquisitions like the MWC as been., More importantly, though, time is not of the essence as it was for the Pac. It would've been a wise short-term move to announce TCU this week, but I have a feeling the yanks are looking much more long-term--further down the road to media deals, BCS numbers, dollars and cents, etc. They're thinking about how their two additions will affect future realignment and the stability of their basketball mega-conference. TCU is stuck waiting until the big wigs in Providence have the stage set just as
they want it. Short-term, this week would've been a no-brainer, but if a TCU-BE union is a wise long-term choice for both parties, then waiting for a formal announcement with the other new member and a large press conference to straight-forwardly address the future direction of the Big East Conference will have the desired long-term effect for the Conference as a
whole, even though it may not provide the best boost to TCU or BE football's short-term interest.