Because Boox won't give you the sources to all the kernel patches that allow Linux to run on these devices. If we didn't need that, there would be no problem, but Linux doesn't have a standard "E-ink" DRM driver so there's no hope to getting this working without a rather intensive reverse-engineering effort.
Unfortunately Boox are serial GPL violators so there isn't much to work with.
AIUI LineageOs is an alternative Android OS. That would be particularly useful to replace GPL-violating software. Why wouldn't that be possible?
Because Boox won't give you the sources to all the kernel patches that allow Linux to run on these devices. If we didn't need that, there would be no problem, but Linux doesn't have a standard "E-ink" DRM driver so there's no hope to getting this working without a rather intensive reverse-engineering effort.
That is unfortunate.
Hisense A9 is an E-Ink phone that supports LineageOS: https://www.reddit.com/r/eink/s/suBlD74nlP
It is pricey but looks great.