Well as it stands running runes isn't the only way of getting Runecrafting xp. Now there is Runespan, a non-profit way of Runecrafting which has more xp/h then any rune running. This has drastically changed the way people go about Runecrafting, most people preferring quick over money, causing people not to run as much.
Tl;dr People aren't running runes anymore and supplies are lower. Demand is still at the same as it was before Runespan so price has gone up.

