Mike Carlin was, to put it lightly, a bit of a stickler for continuity back in the day. It's probably one of the reasons the DCU had its most consistent period of continuity stability during his tenure as DC's Executive Editor. Unfortunately, Carlin also had a habit of sticking to bad continuity decisions, such as nobody knowing Superman's secret ID, no Kryptonian survivors, the Superboy-less LSH, removing Wonder Woman from the founding JLA, and whatever Hawkman became. Rather than just reversing course and admitting that these were horrible retcons, Carlin doubled-down on them again and again.
The decade of creative floundering that Hal Jordan underwent is a perfect example. It took Carlin stepping down and Didio taking over for Hal to finally return as GL, along with the rest of the Corps.