a combination of many things.
player killing is "gone" so many former pkers, rather than unsuccessfully go it alone in bounty hunter, (thus no barraging or god spells, thus no need for blood runes) they sell their runes.
second: since the exchange makes it so easy to sell their runes, rather than stand on w2 for a few hours selling at whatever price was going, which weeded out many potential lazy or slow internet sellers, now they all use the exchange, and since they want the cash fast, they sell lower.
most of the retired pking population selling bloods at minimum price with little need, prices collapse.
on that note, it is now more efficient to sell your death runes and buy bloods, then train with air/water/earth/fire wave rather than the equivalent blast. ^_^
