The Red Cross doesn't set that policy, and has actually suggested changing it. They seem to catch a lot of the blame for it, though, which I suppose isn't surprising considering that they handle pretty much all blood donations in the country.

As Blueberry pointed out below, it's a governmental policy problem.

Hah! There's an idea for a major rationalist project: attempting to increase the extent to which governmental regulators of scientific practice are themselves scientific.