Here is a list of the average viewership (in millions of viewers per nationally widely available game) of every PAC12 team, current Big12 team and future Big12 team over the last 4 years (not including Bowl games since those are under different contracts)

For ease in viewing, PAC12 is bold, remaining Big 12 are standard font, new Big 12 are italicized

1. USC 2.34
   
2. Oregon 2.25
   
3. Washington 1.84
   
4. Oklahoma St 1.79
   
5. Washington St 1.72
   
6. Stanford 1.72
   
7. West Virginia 1.60
   
8. Arizona St 1.53
   
9. UCLA 1.47
   
10. Utah 1.38
    
11. Cincy 1.37
    
12. Iowa St 1.35
    
13. Colorado 1.32
    
14. Texas Tech 1.29
    
15. UCF 1.25
    
16. Baylor 1.20
    
17. Kansas St 1.12
    
18. Cal 1.07
    
19. Arizona 1.05
    
20. BYU 1.00
    
21. Oregon St 0.98
    
22. Houston 0.97
    
23. TCU 0.96
    
24. Kansas 0.76

So 8 of the 10 teams that draw the most viewers are in the PAC12, with only Oklahoma St and West Virginia sneaking into the top 10.  FYI Oklahoma would be #1 with 3.33M and Texas #2 with 2.55. Which is why the two conferences currently get similar revenue. But the Big 12 is obviously losing those schools, which already puts them significantly behind the PAC12 in average viewership.

But it gets worse than that.  Those Big 12 average viewerships for teams like Baylor or Kansas State have benefitted massively from getting to play Texas AND Oklahoma yearly.  Replacing those games with games against Houston, BYU or Cincy clearly won't draw the same amount.  So if we take those games out, the updated average viewership is

1. USC 2.34
   
2. Oregon 2.25
   
3. Washington 1.84
   
4. Washington St 1.72
   
5. Stanford 1.72
   
6. Arizona St 1.53
   
7. UCLA 1.47
   
8. Utah 1.38
   
9. Cincy 1.37
   
10. Colorado 1.32
    
11. Oklahoma St 1.28
    
12. West Virginia 1.27
    
13. UCF 1.25
    
14. Cal 1.07
    
15. Iowa St 1.07
    
16. Arizona 1.05
    
17. BYU 1.00
    
18. Oregon St 0.98
    
19. Houston 0.97
    
20. TCU 0.96
    
21. Texas Tech 0.90
    
22. Kansas St 0.88
    
23. Baylor 0.64
    
24. Kansas 0.47

Now the PAC12 has 9 of the top 10 drawing teams, and the Big 12 has 8 of the bottom 10. 

Obviously the PAC12 would likely fare similarly poorly if every team lost their games against Oregon, USC, etc, but that's not (currently) the reality. If that happens, the PAC12 would have their own issues, same as the current Big 12.

If we take the average of the PAC12 team's average viewerships it ends up at 1.56M.  Doing the same for the Big 12 (without OU/UT) gives 1.01M.  I'm confident that TV executives can also read a spreadsheet.

That's why I don't believe the Big 12 will get a similar contract as the PAC12.

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A few minor notes: 

A) I do think the Big 12 numbers will go up slighlty.  In previous seasons most games with conference championship significance involved Oklahoma.  Now there will be Iowa St/West Virginia games that will have more meaning and draw slightly more.

B) The new Big 12 teams are (with the exception of BYU) not likely to start drawing more viewers.  Looking at averages of national games means that we'd already isolated only their most interesting games.  I'd actually be unsurprised if Cincy and UCF average viewership drop.  BYU is an exception here in that they had so many games widely available that it included a few clunkers, so I expect our numbers to go up.