What would it take for you to like field content it you don’t currently like it?

[VerdeLuck]

That seems to be the problem. Not enough people like the content so they aren't doing it once there are no rewards left that they want. Those who like the content aren't finding enough others to keep the zones active so they're looking for ways to attract others back into them.

Players have become too reward focused. If they aren't getting a "proper" reward for the time spent, they aren't interested. Criterion is an excellent example of this. The content itself has had good response. The rewards haven't and so players don't bother with it.

It's not a problem unique to this game but FFXIV lacks the heavy RNG reward systems that other MMORPGs use to drag out content longevity. It's good in that players generally don't have to wait years to get that one neat item they want. It's bad in that players with more time to play run out of things they want to do faster. There are the occasional players like Supersnow that love a piece of content for its own sake and not the reward but they're the exception.

If you want a quick way to get players back into Eureka and Bozja, add in new rewards that they want and won't be able to get through other methods. It would only be a short term fix since they'd quit doing the content once they got those rewards but those zones would be very busy for a while.

Adding new rewards to those areas wouldn't really work that well at this point. Most people who are done with these zones have maxed out the power in those zones so they would just go right to the activity it drops from, grind it out, and then leave. It wouldn't populate the right areas for player progression.
If you've seen zadnor recently you'll know what I'm talking about, on crystal now Z1/Z2 are dead with maybe a handful of people there, everyone else will be farming z3 fates. What's stopping the people from just going in, doing the one specific thing that they need for the reward, not engaging with anything else or helping anyone else, and then leaving?