That's because there are over 700 of them:
https://patents.justia.com/assignee/e-ink-corporation
None of what you said about the physics of low power displays is wrong, but you're giving E Ink Corporation a pass when they really don't deserve one. They've been unreasonably hostile to basically everybody that has wanted to work with them over the years. No volume price breaks, no prototype-quantity orders (at any price), no partnering with other manufacturers, no shared development projects, absolutely no sharing of the proprietary driving waveforms to groups that want to use a different controller, etc.
Many, many embedded, tablet, even IoT projects that started out wanting to use an eInk display for power reasons had to settle for other technologies because the company just wasn't interested in exploring new leads that weren't one of their existing eBook partners. I can understand having priorities, but you're not supposed to be able to sit on a patent hoard this large while behaving this badly (FRAND requirements, etc.).