Why would that be disabled by default?
Because it enables the Minecraft client to initiate and accept connections to and from Minecraft-unrelated (even Computercraft-unrelated) services on the internet. As far as IT best pratices go, that is a Big Deal and is forbidden by default. Shipping the mod with this enabled could be construed as shipping spyware. And even if not, at best it's still like a car dealer selling you a car without door locks to "help you and your friends get in and out more easily".
No, this should really be something for the user to enable only if they want it. Even the FTB team, when they make custom configs, should ideally not touch that setting.