Some of it has to do with creative changes, but there's also the "what now" situation where the initial story hook wraps up and there's not enough momentum left to transition to a new one.
There's a related phenomenon that happened with Starman, JSA and the post-ZH Legion where the ur-story just kinda stops for a stretch before resuming at speed.
It's understandable but really throws me off when I go to look up a particular installment and find it's Volume 5 not 2.