Well people just are finding other ways to solo the Underworld. Since they made it abit difficult to solo with the Prot bond, people who havent already created a Mo/W are trying to stay away from it. So people are having a hard time selling it back to people so as a result people just sell em' back to the rune trader.
People such as myself just finished the char when they extended the energy on Prot bond so atm Im not sure wether or not Im going to try to make the soloing build, or just something simple to solo places like griffons for exp. Im sure there are many more in the situation of deciding on what theyre going to do with their monks. Maybe more Healers? Heh thatd be nice, but yep thats kinda what happened.
I dont think they nerfed monks I just dont want to solo UW when these Invincible Monks are under such fire. Getting the runes and then getting it nerfed in the future? Great, gotta re-buy armor or gotta get rid of these runes somehow. Something no one wants to spend time doing.
I've noticed that sup runes of all types, not just monk, have been back in stock for a while now. I think those who hoarded them early finally sold them off when they realized the prices weren't going to go much higher than they already were.