So I have been thinking lately, why the 4 member party system?

Everyone who has ever touched a mmorpg should know that Tanks and Healers are rarer then DD's. But in this game, it's like the developers forgot that.

Even with a party system of 5-6 members, tanks and healers where hard to find. But in this game, they apparently think DDs will only be 50% of the server population while the rest will be split between tanks and healers.

So I wonder, why do you think they went with a system that would obviously make DD have a lot harder time getting parties?