Here's an example: over the past several years, e-readers have standardized on 6-inch screens. For all the variety that exists in smartphone and tablet sizing, the e-reader market has decided it must copy the Kindle form factor or die trying. Having used an e-reader before all this happened, I found a 7-8" e-ink screen to be an amazingly better reading experience. Oh well, I'm out of luck. It's not the worst thing in the world, but I'd fix it immediately if I could.
This is in Amazon's best interest; if you buy an e-reader, you're only going to be buying books for it. If you buy a tablet, they can sell you videos and software, too. Amazon has succeeded in pushing several competing e-readers out of the market. They also refuse to experiment or innovate on the design; there have been no significant changes since the Paperwhite's backlighting technology in 2012. Given that ebook sales are no longer growing explosively, this could be a sign that the e-reader category of devices is stagnating.