This article helps explain it:
The Big Ten Network has been a financial boon for the conference. Disaster isn’t imminent, but you could consider the comments by Big Ten Network president Mark Silverman Tuesday as a flashing warning light for not just conference-owned cable channels that funneled massive money into college...
www.yahoo.com
The short of it is that people used to buy cable to get TV period now there is a large segment of the population that has forgone live TV altogether and get their news and entertainment through other streaming avenues. So in the past, if a gamer who could care less about sports bought cable then the conferences got a piece of that regardless but if that same gamer cuts the cord and doesn't subscribe to any Live TV venue then the conferences get nothing. You do this in the millions and it adds up quickly.
Sports channels have a decreasing captive market moving forward. The sports fans will always pay but we have been subsidized by the non-sports fans as well and that is steadily decreasing.