|A Kindle - be honest, does that look exciting?|
I'd say there were two factors at play here. One is that people have increasing availability of other devices like phones and tablets (particularly iPads but also Kindle Fires etc.) that work perfectly well as an e-book reader. It's true that a Kindle has some benefits - it's lighter and it has the e-ink screen which is easier to read outside, and less of a strain on the eyes (not that I find an iPad a strain). But multipurpose mobile devices have become the norm. We no longer want a pure e-book reader, any more than we want a pure mobile phone.
The other factor is that e-ink is dull. I'm sorry, it is. Not only does it show you the world in black and white, it just looks rubbish. Comparing an e-ink screen with an iPad or iPhone screen (* other tablets and smartphones are available) is like comparing reading something printed on an old dot matrix printer with laser printer output. It looks old and tired and grey.
E-readers were the triumph of practicality over style - but consumers are fickle and rarely stick with pure practicality for long. E-ink has begun to sink.