Your examples are misinformed. First of all, you are comparing two desktop environments that have been around for almost the same amount of time. KDE is extrem

Your examples are misinformed. First of all, you are comparing two desktop environments that have been around for almost the same amount of time. KDE is extremely mature, both because of its age and its popularity. This is not the case with some niche e-ink products. Secondly, you cannot even remotely compare the software needed for document rendering with the one for hand writing. The former is a very mature ecosystem and you can just write a UI on top of muPDF and port it to your platform to have a feature complete solution. The latter instead requires a wealth of expertise in how humans write and draw to develop both the drivers and the user land applications. Take the Librem phone or the PinePhone as exampleS. it took nothing to port Firefox or GIMP or DOOM to them, and yet the feel of their UI is terrible. Writing your PIN to unlock them lags, inputs are laggy, moving across the UI is slow and buggy. They are worse than the first iphone from almost 20 years ago, even though plenty of good developers have worked on them