The same thing happened to Green Lantern: The Animated Series and Beware the Batman. The former wasn't selling toys either and it got canned, and the latter was barely promoted by CN and they didn't even bother airing all the episodes before Toonami picked it up a while later.
The reason Justice League Action looks as stylized as it is and has 11-minute segments is probably, at least in part, because WB/DC want a show that can fit better on Cartoon Network.