Money and TV are important to this decision but people are missing the biggest reason for this expansion.
It guarantees the Big Ten will not become like the Pac 12. Meaning We're not going to be landlocked.
Look at the Pac 12 in expansion right now, they aren't going to get anyone from the Big 10 to defect and they learned with the Texas situation that going after the Big 12 South isn't going to work either, in terms of expanding the Pac 12 is kind of screwed.
We were in danger of having that same situation happening.
What this move does is assure the Big Ten that if expansion hell breaks loose and everyone heads to 16 team confereces (it will eventually happen) that the Big Ten is already in prime position to attract viable east coast markets and teams and not get stuck choosing between raiding the MAC, Picking up the leftovers in the Big East or teams like ISU, KU or KSU.