It's because BRD in 2.0 had to sacrifice DPS to replenish resources for MP/TP regen for the party. These were slowly phased out. Then they decided casting songs no longer made sense since that's time spent no longer DPSing. Since this isn't a game with Support Classes, they reworked the songs to just be "stances" that confer a slight boost to raid DPS. They cannot make BRD a true support job as it was in other games because that's not a role that exists.