Like most of the FFXIV player base I would suspect the answer to the OP's question would be rewards and nothing

at the moment the rewards from PvP is not enough for me to queue up for PvP since for me personal I don't find PvP fun

I mean the upcoming Garo x will reduce down the queues for a week or 2 after it hits and then you will be back to the 60 min queues again
the GC restrictions on FL I think is a red herring

unless you can get people like me interested in PvP you will have zero hope of any real solution to the PvP queues

I guess for me is I can be a sore looser and being matched up with people who live and breath PvP and will rub it in your face, terrifies me and yes I do know there are systems in place that should prevent this but due to low number I would suspect these are not working effectively