If they lowered the GCD they would have to rebalance every single battle in the game as players would be able to chew through mobs at an alarming rate. I realize that recent MMOs have done little to counter the fostering of an "I want it now Mommy NOW!" generation of gamers who's patience can now be measured in halves of a second but slowing the content down does open the game up to a lot of older gamers to enjoy it as well as make decision more tactical rather than simply twitch based.