As long as SE keeps milking the dead cow, they won't merge, people keep transferring server's to buy gear and move to more populated server's just to move somewhere else.
I think the game is going better than SE expect when they said they would look into merges after the end of console support...so I would wager that they are on hold at the moment.
Not everyone is interested in merges, those that do have the payment option.
SE probably perfers self merged servers like Asura than random player who doesn't post on reddit or visist FFAH getting frustrated because their server has a 2 hour line for ambush.