NBC (and the other broadcasters) provides copies of its shows to Youtube's Content ID filter, which is supposed to protect copyright by blocking uploads of videos that match ones in its database of claimed videos. That means that if you own the copyright to something that is aired on NBC, any subsequent attempts by you or your fans to upload your work will be blocked as copyright infringements, and could cost you your Youtube account.
The latest casualty of this is the video game Beat Saber. Jimmy Fallon played part of one of Beat Saber's levels, and so no one else cold upload their own gameplay of that level to Youtube without being accused of copyright infringement and blocked. After a lot of fast work by Beat Saber, they managed to get the ban lifted.
The EU just passed a new Copyright Directive that mandates Content ID-style filters for all kinds of expressive speech (video, audio, text, images, code, etc) for every service.
Beat Saber Stream Blocked by Jimmy Fallon Show [Jimster71/Reddit]