What would easily fix this is allowing all servers to help one another during these FATE. SE should have known just how much the content would drop off once everyone got the loot they needed.
Because acquisition of loot is as easy as it is the drop off it going to crater because there is no economical incentive to continue with the content when everything is going for pretty much nothing.

Since there is no secondary economy for the materials and the only economy is what is gained through the lunar credit shot or the Cosmic Credit roulette, people are just going to stop engaging with the content as it no longer provides them with anything rewarding.

The only people who are still engaged with this content are achievement hunters, people still farming their relics and the niche crowd that enjoy crafting and will willingly engage with this content until it's complete, not to be mistaken with the niche crafting/gatherers who got what they wanted and are no longer invested with the content.

An economy beyond loot rewards needed to be setup to keep this content alive. The ability to make gil off selling gathered materials or selling medicines/food that specifically work within Cosmic Exploration. Anything to keep players engaged but when the only thing keeping players engaged is bringing up a progress bar that has no feedback based on the different quest you do, people are just going to stop doing the content because it isn't fun to have no system in place where during X phase these missions will count more towards rewards and progress, a very basic concept that would keep the content engaging and at least inspired some people to focus knowing that by doing these missions they are providing more progress towards the next upgrade.