That hurts, doesn’t it? It may even send you into a cold panic, when you know that a particular piece of communication is of importance to you!
Video is content. If there is speech in it, and you don’t provide closed captions, you lock out people who can’t listen to it. Either because they are deaf, or because circumstances don’t allow turning on sound.
By the way: Google loves closed captions too.
I wrote an article about why captioning videos is beneficial in more than one way.