Well see you are forgetting the differences between Abyssea and using GoV

In abyssea you use stones for time. You have to kill them in a specific manner to get the chest of choice as well as time to stay in the zone, and you are restricted by the time you can spend in their if you don't keep time chest upkeep high

GoV on the other hand is open, you can grab a page and spam it without having to run back to the book, you have a chance to get augments with each completion and you can stay there for as long as you like. Which means you could technically make a mule character that never leaves the zone and thus has all the possible buffs possible and increase your odds of chest drops.

Basically the reason why they won't change it is because Abyssea has more restriction compared to GoV. Because of those restriction of course the chest drops would be better. If GoV had the same loot mentality then perhaps people would op to go to GoV to get the NPC items since it's worth more then in abyssea which would be imbalanced. If you want NPC items that fetch a lot of gil go to Abyssea, but if your objective is to obtain the special item in the zone then just accept GoV for what it is lol.