Wait, Cartoon Network forced him to stop speaking? What on earth for?
Apparently, they actually thought he talked "too much" during the first season, and they felt it "wasn't right for him to talk so much", and basically just went up to John Dilworth and said, "We don't like this, will you change it?" Hence why afterwards, Courage just basically babbled incoherently, and if he ever did speak, it may have been a zinger or two an episode (and not EVERY episode, mind you).
The thing that bothered me the most over that was Courage not even talking as he was typing on Computer... then, you pretty much had to guess what it was he was saying or trying to look up.
Ironically though, Courage still talked in the Cartoon Cartoons comic books... matter of fact, THOSE jumped the shark as well when they switched to that "Cartoon Network Block Party", because it's like they stopped caring about to attention to detail, and suddenly, the comics were incredibly plain, simplistic, and lazy, as opposed to actually using the surreal photorealistic design like the series' proper did.