I'm sure there are tons of reasons. You have the stupid people who don't care, you have the people who will undercut just about anything to make the smallest sale, you have the people that do it trying to bait people to lower prices so they can mass buyout, you have the bots for RMT. Also add in that the crafting system in this game is just about pointless so raw mats don't move to fast for the most part. Heck I could go on....

Can you fix it? Yea but it would take a radical effort on SE part but they wont ever do it. You can thank the ease and speed of leveling in the game, the ease of obtaining gear from dungeons, and SE's failure to actually go after gathering bots.

Every time I go look at sometime that moves decently quick, all you see is massive stacks sold by the same person. Heck just go look a the crystals, its fairly obvious who the gathering bots are but do they go after them? Nope. I loved when I catch the invis, teleporting, instant node farm in one swing gathering bots. Made me sick to my stomach. Funny thing is, I tested how oblivious people were to it by asking others who were gathering in the area if they noticed the bot. Most of the responses I got didn't even friggen see them at all and just thought it was a bug they saw and ignored them. Hey did you ever wonder what you saw the graphical gathering flash and no one was there derp!