It's not patents, it's literally artisanal handcrafting prices - they produce these giant e-ink screens by fusing together 4 smaller screens, and they do so by hand because there's almost no demand for $1000 1Hz screens, so they haven't automated the process.

>just about every other display tech came down in price by a factor of 10 a few years after it was invented.

No, the successful display techs came down in price. The commercial flops that nobody hears about are the same price as always (i.e. astronomical), because they have no economy of scale.

That is so much more than just patents. Vast engineering effort and process investment back up every "economy of scale". Unfortunately there is something about most e-ink designs so far that doesn't scale up in size very well. Really small ones are already cheap.