Cable channels regularly get dropped from lineups due to disputes over fees. Here’s a recent example of NBC in threat of being dropped. https://www.pressherald.com/2019/10/02/spectrum-may-drop-nbc... Edit: that link has a paywall, but here’s another discussing cable channels being dropped https://www.post-gazette.com/ae/tv-radio/2016/02/14/TV-Q-A-D...
There’s no general right to force cable providers to have your cable channel.
Fox and NBC cannot provide air time for one political campaign and deny air time for an opposing political campaign. Twitter is more like Fox and NBC rather than Comcast.
Fox and NBC are only required to provide political campaigns equal access because of their licenses to exclusive use of portions of the public spectrum.
Cable channels like CNN and Fox News don't use this spectrum, and thus don't have the same requirement. Twitter is more like a cable channel than a broadcast station.
Comcast can't block CNBC or Fox and at the same time nobody assumes that Comcast is responsible for view expressed on the networks it carries