I've heard it's quite simple: the browser was only ever included in the first place as a way to log into public Wi-Fi networks like coffee shops which have a screen you need to log in through.
As long as the browser is good enough to log you in, Amazon's happy. Which is why, after almost 10 years, I think the browser is still labeled as "experimental". (At least last I checked.)
I’d get voicemails (transcribed) and text messages to my Gmail and could text back from there. Gmail even had a lite version that worked quite well on the Kindle’s experimental browser. Fortunately, my needs for making/receiving an actual call on-the-go were nearly non-existent so it worked quite well.
Was really sad when they pulled the plug on the free 3G.
> The ESP32 is a microcontroller that has very little RAM and isn't quite suited to deal with HTML and such. So I had to use a Raspberry Pi as a rendering proxy and transforms the RSS and the text on the page so that the ESP32 can digest.
The Kindle doesn't come with a lot of onboard horsepower, and putting the same class of SoC as a Raspberry Pi in one would likely increase cost and have other tradeoffs.