I don't think it's that they can't handle more than one thing. I think it's just that they want to focus their attention on the new movies. Makes perfect sense to me.
If they can handle more than one thing, why does focusing their attention on new movies mean they can't also focus their attention on something else?
Wasn't there at least one book or graphic novel that depicted former Republic Clones who were still alive during the time of the Empire and the OT?
I don't think it's the one you're thinking of, but Luke Skywalker and the Shadows of Mindor
is set around a year after ROTJ and features a clone who's been in action since Geonosis.
This article says Lucasfilm has assured fans that the dismantling of Lucas Animation does not mean we won't get the final Clone Wars episodes we were promised.
Well, that's a relief. For a second there I thought we were going to get out of TCW without them fucking up Order 66 because some fedora-wearing douche can't follow AOTC.
Dodged a bullet there!