Poverty. If you have no income, and $X in savings that produce 5% interest, if 0.05X isn't enough to live on, you're still going to live on the money you have, even if you're aware that it will run out.

I think farmers in developed nations are much better off, but that farmers in the developing world are depleting topsoil faster than we can afford to have it depleted, to say nothing of the future cost to themselves. I further am under the impression that topsoil depletion is still a problem in the US, and its current resolution is forcing faster topsoil depletion in the rest of the world. If you have specific information that this is not the case, I'm basing this impression off a large number of things that I've read that all might be out of date, or collectively too pessimistic about current conditions.

Edit: also note the last paragraph of my reply to Vaniver.