For the record, the "patents" think has no links to back it up either.
But to answer your question: E-ink screens are less than $100 (depending on the size), that's already pretty cheap. They're only expensive when compared to LCDs. LCDs are produced at a rate of billions per quarter*, with ~6 billion smartphone owners, and lots of them having multiple LCD devices e.g. laptop/desktop screen, work computer's screen, supermarket kiosk, tablet, smartwatch, car screen, etc.
In contrast, e-ink screens have basically three applications: e-readers, e-notes (which is basically just an e-reader with a stylus), and supermarket pricetags. E-readers/e-notes are a luxury item that you don't need if you already have a smartphone/iPad. There's just no economy of scale for e-ink; not compared to LCDs.
Because there's no economy scale or obvious new markets to expand into, there's not much budget for R&D, so the entire field moves slowly.