I chatted with the guy from Visionect about this once and he said that it was basically all about scale. There is massive demand for the panels that go in those generic LED monitors and many huge factories dedicated to making them.
The eink display looks gorgeous, by the way. But it's not a computer monitor and doesn't claim to be.
You'd think there would be a large market for signage, and the process for manufacturing electrophoretic e-ink screens isn't that different from web printing (rotary presses), which is both mature and scalable (in size).
I think eink does not perfrom well in freezing temperatures which removes a lot of large format addressable signage market. Otherwise I'd expect economics to drive cheaper large format eink screens
The eink display looks gorgeous, by the way. But it's not a computer monitor and doesn't claim to be.