You don’t need to be a rocket scientist to work this out.
A lot of players here came over from WoW.
Are they avid star wars fans ? Probably not.
WoW is near the end of its expansion, no new content very little reason to go back.
Blizz will want these customers back, so by offering them a better experience as in cross server lfg and cross server easy raids, new content there will be a mass exodus.
So for a short while a realm based lfg tool might be ok but not indefinitely.