it seems like no one ever goes into these battlefields. Why's that?
From what I've read, you get lousy exp playing support (think healers like WHM, buffers like BRD), but front line jobs won't last too long without support. Moreover, if you don't get enough exp, you can't even lot the items from treasure boxes.
It's a bit like Campaign Battle, where the reward system encourages everyone to be out for himself and himself only--except the battle system don't let anyone advance very far without teamwork.
Damned if you do, and damned if you don't.
Maybe it's not what I think it is, but on forums/FFXIclopedia it sounds like it's great for multi-boxed people wanting stuff for their main characters (and don't care about their boxed WHM or BRD or RDM), but sucky for everyone else.