Sanderson's been stuck for some years now writing someone else's grand finale and his big series before that was Mistborn which doesn't suffer much from the cited problem. Sanderson really likes to build his worlds and magic systems and he can't do that at all in WoT nor does he really have the ability while he's writing it to really buckle down on one story so I figure he's probably venting via novella, so to speak. So I think when WoT is truly totally done, tours and all, we can expect some better quality to start returning.