Because the game actively encourages people to pull lots and pull fast. In fact it rewards you for doing so, not to mention years of people running ARF over and over and over and over hell even now with the Moogle Tomes we have 8 man BLU groups who clear out Bahamut Turn 2 in what, 7 GCDs? The game does everything it can to ensure we do this. You want slow? Squadrons and Trusts are there.