Possibly the instability comes from the fact that the crypto market overall is still very volatile because of it's relative nascency and very small volume as compared to the established fiat world.
But I"m just parroting, I don't really know of these things at a deeper level.
I understand, and I am pretty much "just speculating" on the whole intent. It's a long way from an idealistic vision to street-level reality.
I'm just hoping someone with some expertise will come along and read this, and leave a comment I can make sense of!