Comcast/NBC is attempting to position itself as a competitor to ESPN, which is the behemoth of all cable networks and especially sports. NBC wouldn't necessarily be "paying up" for Cubs/Hawks without having to, but rather positioning itself to dominate the Chicago sports market for the next generation. The thought is possibly that while they are making money off of CSN, that agreement runs out in a couple years and if they aren't involved, that network could conceivably disappear with the four teams making arrangements with other networks. Comcast doesn't want other networks in Chicago, so, much like a team that locks up a pre-arbitration player to a favorable contract, they could keep the Cubs on board and on their family of networks by making them an offer that is considerably higher than the current deal while still lower than what it would theoretically cost to let them become free agents in 2019.