The Pac-9 (8) had no shot of hitting 1.7MM subscriptions and they wanted linear exposure. I think it's pretty simple. When you consider the MLS has under 1MM subscribers with 29 teams in major cities (and even a spike due to Messi) they are nowhere near 1.7MM. And they have a lot of free subscribers due to T-Mobile.
Let's assume they expanded to 12 (and Arizona stayed -- but they were already voted into the Big 12 by then - but let's just assume that.) Pac-9 adds SMU, San Diego State and UNLV. So 1.7MM / 12 = 142,000 subscribers per school on average. Just think about that for a second. SMU averages 20,000 fans for football and <7k for basketball. And remember this is subscribers not total people (a family of four only needs 1 subscription.) Let's say optimistically their fanbase is 80,000 strong. That converts to MAYBE 40,000 subs (people willing to buy apple+ PLUS the additional fee for Pac 12 content.)
Even if you assume the strong brands in the Pac 12 could get those 150k subscribers (Arizona, Washington, Oregon) there's no shot the other 9 with apathetic fanbases were going to cover the rest. No one cares about Cal, SMU, UNLV and San Diego St. OSU/WSU have passionate fans there's just enough of them.