Norte Dame would be totally out of place in the Big 12 and alienated by the rest of the conference. They have no past history with any team in the conference. I know ND recruits nationally but joining the Big 12 wouldn’t do any favors for their recruiting. ND wants to stay east of the Mississippi where there are more viewers. I am glad we are in the ACC for the same reasons.
If it's history/region, then it's the Big Ten. Michigan and Mich State is their big rival. Indiana & Purdue are in-state rivals. Illinois and Northwestern are in that Chicago market. History with Nebraska. Even the Pac-12 has USC & Stanford, which are two big historic rivals.
ACC is more of a East Coast league. The only real rival with history for them is the Miami game and some other history when FSU was relevant. With FSU being down, they may see the ACC as the easier league they can run through in football. Clemson is their only big time opponent.
Big 12 gives them Texas and Oklahoma as big draws. Kansas, K-State, Ok State, and Iowa State are all mid-western programs in the area. The Big 12 also lets Texas have their own network and power, so they'd have more autonomy in how they can negotiate TV deals.
WVU isn't too far and it would give them a closer opponent. Although I hate WVU, they make way more sense in the ACC. Glad they went Big 12 and we didn't, worked out well for us!
To be honest, if a league let them negotiate their own TV deal where they got the NBC deal, it would still benefit the league. They could get all their home NC games on NBC and then split their conference home games. Then the other 4-5 road games a year would all be for ACC/ESPN, which makes the deal more valuable. Not to mention the conference title game money they'd get.