NBC is owned by Comcast. Comcast currently won't broadcast Avalanche or Nuggets games in the Denver metro area because of a manufactured contract dispute with Altitude (KSE owned network that owns exclusive local rights). There's significant speculation that Comcast's end goal is to start their own local sports network in the Denver market, and are trying to use their monopoly in the cable market to put financial pressure on the station who currently hold the broadcast rights for both the Avs and Nuggets.
Based on this, I wouldn't be surprised if NBC is shutting down their national channel (NBCSN) because they don't want to compete with the local broadcasters who hold the rights, and intend to replicate their ploy in Denver around the country.