I think their line of reasoning was that the people that watched SD didn't stick around to watch anything else on the network, or something to that effect.
There were a few CW/UPN/WB shows I actually watched and they all got canned. Not for poor ratings, but because it wasn't the type of audience the network wanted to attract. This was pre and post merger. If Chris Rock wasn't so involved with With Everybody Hates Chris, that would be gone too.
I've deleted the channel off my tv permanently.