The only migration route on the flagship server of the game is out from world 1, with like 100 players left and should have closed 4 years ago.
The choices for fort fighters on .net are between an old world colorado, that fills their battles with lots of high level offliners, or a newer one unfortunately with up to 3 low quality battles per day, which kinda died when the newest world was opened and half the player base left.
Both of these worlds can only benefit from migration, boosting online numbers in battles, and giving duellers more targets. I can only imagine other servers have similar issues from what I've read over the last 2 years specifically. People want to play on active worlds but aren't willing to give up their beloved characters or start again to do it.
Personally I wish the "recommended" world on servers was the most active PvP world rather than the newest one or whatever it is now, giving new players the best experience possible before they decide to take a dive into the perpetual disappointment of opening a new world before the last one has had a chance to hit its peak.