I dont think theres any specific reason as to why its been closed for a while
I did have a suspicion that with work starting on a new pier in the gates 12, 13, 14 area that it could be to re-route passengers around any building work, but i havent seen the plans yet.
Im guessing that with central search moving back to the escalators the gallery, if it does stay will most likely just be for those who are airside