What is holding this technology back?
E-ink patents and monopoly due to those.
The Very Slow Movie Player: https://debugger.medium.com/how-to-build-a-very-slow-movie-p...
It needs to be built/assembled yourself, however there aren't that many parts involved
It seems that every now and then a product like this starts a Kickstarter campaign, or there is a blog about a DIY project; but so far I haven't seen anything consumer friendly and available for purchase.
The closest thing I could find was https://framelabs.eu/en/artframes/ , for which I could not find any reviews, plus it says:
> The device is delivered as a kit and can be assembled in just a few simple steps. No tools are necessary for the assembly except a screwdriver.
If you mean "why are there no colour e-ink displays" then a) there are, and b) if you look into how e-ink works it's pretty obvious why it is so difficult to do colour.
https://thepihut.com/products/inky-impression-7-colour-epape...