I don't actually know the reason for their disabling, But I can state that that's not the reason. Enderchests are personal to every player, Meaning every players enderchest is only accessible by them.
Well to be honest if they were used in Warworld, wouldn't that just get rid of the point? Like if people come raid what is there to grab ?
It would make Warworld a lot less popular and would become boring.
I personally think the rule of not using ender chests should stay the same.
I completely agree with whosurdaddylol. Noone has complained about not having ender chests and they have been disabled for a long time. War world is a great example. Having enderchests would be the same as having the player vaults plugin. Its pointless and eliminates the point of raiding factions. But in survival it would be good to have to save your valuables ( Diamonds, OP gear etc). But i still think that Ender chests should stay disabled.