I didn't realize demographics were so important. I always thought it was just the base numbers that were important, and the demographics were more of just a bit of interesting side information.
Nope. The money to make shows comes from advertisers, who pay for commercial time on those shows because they believe it will get people to buy their products and make them a net profit. So they want the shows to appeal to the particular category of people that their products are aimed at. Getting lots of viewers won't help the advertisers if those viewers aren't interested in buying what the advertisers are selling.
Although CN does seem to be bizarrely narrow in its choice of advertisers these days. As I think I said already, instead of cancelling popular shows that don't fit their sponsors' preferred demographic, why not just get more sponsors with a broader demographic focus?