> As soon as you mention file, you've lost a lot of people.
Attaching documents to an email is the one thing most people can actually do because without it you're unable to deal with your insurance, doctor, tax guy or what have you. In addition to web browsing it's the only thing my boomer parents with very few computer skills have figured out. You basically bureaucratically die otherwise in the modern world
The biggest issue is that most people probably don't know that Amazon even offers that feature, they I assume intentionally don't really advertise it much.
The average person: "Fine, then I'm just going to be unable to deal with my insurance, doctor, and tax guy."
I think it's more that people don't know that you can get ebooks as files from other stores to begin with. But then also you need ones that don't do DRM, which complicates things further.
But, yes, Amazon is also deliberately vague regarding those emails. Most of their documentation presents it as a way to "keep your documents in your Kindle"; the fact that books are a subset of those documents is not exactly highlighted.