Okay, It's Two-Way Communication Time

[Geryth]

That, too, is primarily because of healers. ... With healers around, though, people just don't bother, if they fight at all, they fight after the ice is done, because killing anything takes way too long to be worth it. ...

You can put a bigger incentive on killing players in Shatter easily by transferring the ice credit of a player to the killer if you manage to kill a player. But I can already tell you that even that would not be enough to make people attack each other on the ice if healers are present - it's just never worth it.

This is so absolutely true. I've been playing a ton of BLM lately and since ice has 50% magic resistance, my main goal when ices are up are to look for enemy players to try to pick off. There seems to always be one jerk of a healer that follows players to side ices. And unless opponents are dumb and trickle into big ices, there will always be healers at big ices, and since most DPS are on the ice, I can never out damage a healer solo even as a BLM. So I find in many situations where I would love to be able to wail on enemies for some PvP goodness, the presence of healers largely makes that a wasted effort, and I'm losing our team points if I'm not putting my awful magic DPS on the ice.

...and I may at times frustratingly pound on someone who's just getting healed for no other reason than to inflate my damage dealt for the match.

...and I may at times have a lot of fun foregoing any DPS, particularly when ices are up and can freely do this, to run around and sleep all the healers and ranged DPS for funsies (I do tactfully sleep healers when possible to allow my team to secure kills, but many times it's very dangerous as a BLM to get that close)