I think most of it had to do with the security holes that he refused to fix that left a bad taste in peoples mouths. I think it had to do with https://bugs.launchpad.net/calibre/+bug/885027 etc.
nice article; I don't really find it that complicated, only extremely useful.. In fact without it i would be quite the sad panda especially as I'm still required to support IE11 for foreseeable future in many large apps. But ya, if you don't need it don't use it. I'm sure as heck glad all the tooling I have now exists though!