On the other hand iPad is more general-purpose powerhouse for pretty much anything, but if I'm between this and iPad for reading some books I'd prefer this. And I use/love an iPad Pro+Apple Pencil. Still would consider this for my long book/blog/paper reads.
Also if you try buy an e-ink screen as a part for a project you'll see a difference in price, which will no doubt be a factor too (though the difference you or I pay for a single unit might not be entire indicative of what is paid for bulk/regular orders by manufacturers).
which make them worse in almost every way to do the things an e-ink device is built for.
You also seem to be making the mistake that products should be priced according to their raw manufacturing costs. Not only is that ignoring engineering, marketing, legal, licensing and other costs, it’s also ignoring profit and trying to recoup investment on an initial product which itself is risky without knowing how well it will sell.
You are correct. 2021 alone would have sold well over a billion smartphones each with a display, OLED or LCD.
2021 was a banner year for ebook readers and yet I'd doubt they even reached 10 million units worldwide.
Electrophoretics just doesn't get investment because plainly speaking, the physics limits what it can do, and so nobody wants to invest big money into it. You'll see startups come and go, picking up maybe a 100 mil here and there and then burning out. That's even true across other display tech. Liquavista died. Qualcomm mirasol died.
You want improvement, somebody has to risk big money.