I think this is what they forgot to do. They added in content in which for the most part you can pretty much gear to i110 without even having to touch coil which means for the most part, doing coil isn't really as needed because you can gear up to i110 through other means that don't force you to fight over sand/oil drops and that's the big issue there.

if I"m not mistaken I think sand/oils came maybe 3-4 a coil group, which means only half the group could obtain upgrades.

Now there is a system in place that just does away with that, honestly since they added these 250 allied seal items maybe what they should do is have coil give everyone a free 250 seal book, that would draw people back into doing coil because it would be a guaranteed drop and encourage players to do said content.

There in lies what they forgot to do, they forgot to alter/add to the loot pool of coil when they pretty much added content that replaced coil since it is an easier method to obtain tomes mainly because players don't have to fight over who gets the book or wait til there turn, everyone can pretty much obtain them at the same rate which makes teams working together pull away from coil because they can instead use hunts as a quicker way to gear up their players.