For a very long time Blizzard has not allowed ordinary quests to be done in a raid group. When asked, they've always said that they feared everyone always joining large raids to steam roll content. In a lot of ways, it looks like FFXIV is proving this stance correct.
In the last patch, FFXIV introduced Hunts. Throughout the world, there are named monsters running around. The monsters have different difficulties: Rank B is roughly tuned for a 4-person group. Rank A is an 8-man group target, and Rank S are rare and require multiple groups.
However, SE did not include tagging with these mobs. Anyone who gets a few hits in gets credit for the kill and the reward.
So the etiquette that has developed is that if you find a Hunt mob, you announce it to the zone, wait for everyone to assemble, and then zerg it down. Doing this has made Hunts into the optimum method of getting endgame rewards, which has pushed even more people into doing them. You can actually see the effect on queues for instances and dungeons, as they are much longer than before.
Of course, since so many people are gathered in the zerg, there is no challenge. Interestingly enough, people who play late at night or early in the morning report that Hunts are a lot more fun when done in small groups, closer to how SE intended them to be done.
The obvious solution is to enforce tagging. Yet that might lead to uncooperative gameplay. I joined a guild group that was going after a Rank A in one zone a couple nights ago. We advertised in zone chat, and ended up with a full 8-man group and 2 others. It was nice that those two others could still participate and get rewards, rather than be left out.
SE could also greatly reduce the rewards. But then doing Hunts "as intended" is no longer a decent experience.
The other idea I've seen is to make Hunt rewards a "once a week" thing. You can only get rewards from a given named mob once per week. This is probably the best solution. It doesn't stop the zerg entirely, but it does thin it out.
All in all, FFXIV's Hunts are a cautionary tale for MMO devs looking to make world content for small groups.