Uh .. emperor's gear can be bought cheaply from an NPC.
Putting it up expensively on market board isn't too different from ripping off new players unaware of the NPC that sells them.
I know some players that actively work against that by putting it up for same/less than the NPC sells it to counter this.

Can't really comment on the other parts, but I assume it just has to do with the recent influx of players. More players playing = more stuff being sold (though could also mean more stuff being bought, depends fully on supply / demand of each respective item).