The answer is not just crafting materials being dropped from boss chests.

It is a combination of mats dropping from boss chests, hunts giving far better tomes-to-time ratio, new dungeons not able to be speedrun-ed as fast as Brayflox could be, general rise in difficulty of new dungeons and last but not least, Sands of Time.

All those factors compounded together simply cause people to turn towards the hunts for better rewards for their time.