The game was originally designed with everyone connecting to Japan, but the unbearable delays for the US region players during beta testing made them change the plans and create the US data center. Then at launch the login rush that happened which happens again at every maintenance made them change the lobby structure, and finally the stress on the cross-realm Dungeon Finder servers made them separate each data center into server groups.

To re-merge everything back is to throw away all that progress and delve back into chaos that we have left behind.

Personally, I don't do the low level roulette anymore on my 50PLD&WHM because the meagre 5 Poetics is a joke, and the 7500 gil role bonus isn't worth giving up the time I need to spend idling waiting for the daily mob hunt FATEs. Some FATEs would take up to 1 hour to spawn. The lack of housing plots for purchase means that 7500 gil isn't of much use to me now anyway (got 4 million gil but no S plot to buy---the system itself devalues its currency due to extremely limited supply of its biggest currency sink).

For people still leveling, the daily roulette exp bonus is good, but the role bonus simply isn't worth the time, and the frequency that level 15~17 dungeons pop is just too much to bear. So on my other battle classes, I'd rather just run FATEs than do my hundredth or so Sastasha run. When I do want some dungeon drops, I designate the highest level dungeon I can do, because anything below that would only give me rubbish anyway.

For capping Poetics for the badly geared, the low level roulettes are also a joke. Spamming Sycrus Tower is easier and faster (15 Poetics), not to mention it gives you iLv100 gear and Sands and Oils for upgrading Soldiery gear. And if you're geared, just do an Expert Roulette a day and you're done.

The root problem is simply content getting outdated. You can only force people to do old content to a certain extent, beyond that you are going to lose customers. The static nature of all content in this game means there's virtually no replay value to the content itself---not even difficulty because all the leveling dungeons are positioned as learning dungeons, tuned to be easy mode for even the average MMO player. Virtually the only reason to repeat the same content is for the rewards.

So the only solution really is the NPC party solo plan, which I guess probably will not be implemented until late 3.x or even 4.0.