RMT are doing this. Ironically enough, iron plate is exactly one of the gear sets they've targeted on my server.
The mats, well, the mats are easy to get because the market is flooded with mats farmed by bots in addition to those sold by legitimate players.
It's a snowball effect. Say they only farmed crystals. That = cheaper/plentiful shards/crystals = cheap/plentiful shards/crystals for grinding = more crafters hit 50, and faster = more final products flooding the market. That's the ripple effect from crystals/shards alone.
It's basic supply and demand. Something I wish more people understood so they'd stop undercutting by 50% of the next highest price.