I don't know why these places don't consider reruns. I mean, that's what they were doing with the ABC Kids line up, essentially showing reruns of shows on cable.
The closest thing to rerunning is CBS was rerunning the 1999 Sabrina the Teenage Witch cartoon (and that wasn't that long ago... of course, it was always the same 10 episodes, and they NEVER aired the one with Weird Al in it). Cookie Jar reruns Inspector Gadget and Heathcliff among other things on digital channel THIS (even though, like most things, they refuse to air more than a handful of these episodes... there's only 10 episodes of AOSTH they run, when they have a library of 65). And with the Cookie Jar This rerun line up, it's ENTIRELY funded by PSA's and the occasional mail order product. There is NO excuse.
In the old days of Saturday Morning cartoons, even up until the 90's, they had decades old cartoons. Speed Buggy (never saw it, and I don't care to see it) had one season that was rerun for years. even 4Kids with Sonic X. Disney has a large back catalog of shows, especially ones that have the TV E/I claptrap that they apparently need. Pepper Ann, Recess, Lilo and Stitch... they could all found an audience and gotten decent enough ratings without the need of all this funding from commercials that child advocacy groups unfairly single out.