Why is closed captioning always so f***ed up?

I was watching a show with closed captioning on (something I don’t usually do but I couldn’t make out a couple of mumbled words so on it went) and I was immediately thankful that I wasn’t deaf. I feel for those who rely on closed captioning for content. I guess I can kind of understand the need sometimes to cut out a word here and there in order to shorten a sentence. What I can’t understand is all the typos and gibberish that it spews. Often times it makes no sense at all. Haven’t we had CC long enough to provide a quality product? Or are we just marginalizing a population that can’t hear?