Because it was horrible. It sounds like a good idea, but this is what it really boiled down to:
Pre-invasion: Everyone sits around by the NPC, waiting for the last second in an attempt to snipe first place so that they get the guaranteed drops. If you didn't have the backup of all your FC crafters (or tons of money to purchase items yourself), you would never place. At the last second, everyone would dump all their items and pray to God that they had the most.
Invasion Phase 1: While you could mix it up and do fun things like all DoW or all crafters, it rarely happened. Generally, it looked like this: Your party was comprised of 1 tank, 2-3 healers, 2-3 DoL and 2-3 DoH. DPS? Those were the NPCs. The tank would taunt mobs off the DoL and DoH whenever they pulled aggro (which was a lot) and pull enemies closer to the middle of the NPC archers so that you wouldn't have archers standing around doing nothing. The healers would stoneskin/regen the archers (SS/regen was extremely powerful in 1.x, nowadays you'd just heal like normal, probably plant a fairy in the middle of them). DoL would run around, picking up flasks and turning them in to cause debuffs. DoH would sit around, crafting stuff and turning it in for specific buffs.
Invasion Phase 2: The boss shows up. This is where things get...well, even more boring. The tank goes and picks up the boss and immediately pulls him far away from the archers, because as soon as the boss dies, the Hamlet is over, and to maximize points (and rewards), you need to let ALL the enemies die first. This generally meant the tank would run around a tree for 20 minutes, or run up and down a cave for, or just run around. Whatever. With the exception of the cave, he didn't even need heals, because the boss would never reach him. Everyone else just continued as usual. Finally, you finished off the other enemies, pulled the boss into the archers, and won. Hurray.
TLDR: It was boring as all heck. It would have to be completely redone. The idea was good, the implementation was not.