As for the prices of everything else under the sun: supply and demand.
Take harvested logs/ore/etc. There is an influx of materials on the market since a lot of people leveled a botanist/miner to 50 so they can get maps and dumped all their harvested items on the broker.
Also, the big rush of the server population grinding crafters to 50 is waning. The demand just isn't there.
Think about pre-50 gear: Dungeons give Aetherial gear which is iLvl+2 or +3 and better than the similar level HQ item. People are grinding these to level. They don't really need crafted gear to level. Maybe the odd piece if they go 10 levels without a ring upgrade.
Also, think about the ease by which people got crafters to 50. I feel like every 10 seconds someone is shouting in town that they have all 8 crafting jobs to 50 and they are selling their services (that no one wants) for a couple gil. Too many crafters. Too few customers.