You are perfectly welcome to share the medium itself (e.g. the ebook reader), it just so happens that with physical books, the medium lends itself (pun intended) to sharing.
Either way, you actually don't own the text in the same way, as amazon has demonstrated that they think they have the right to revoke your account and therefore access to the data.
There's a mixup in terminology here. We're not talking about lending the medium the book is printed in. We're talking about copying all the words over to someone else's machine, maybe with a promise to delete it on your own machine. The thing is, the right to copy the contents of a book is restricted by copyright and can only be done with the permission of the copyright holder.
So let's rephrase this to be more precise:
> The tech to lend or entirely transfer the contents of a paper book or an ebook via copying is clearly there (some books can be lent once for two weeks), you are operating in an environment where the vendor does not allow it.
And yes, exactly. Both for print and electronic books, copying the words and sending them to somebody is not allowed without the permission of the copyright holder.
You don't have to like the system, I certainly have issues with the system as it's set up. But it's perfectly obvious that under any standard interpretation of the concept of copyright, it means that the copyright holder has exclusive rights to the copying of the content. Lending ebooks involves copying, therefore it must be licensed by the copyright holder.
--edit-- also the fact that you can onmly ever transfer any data in electronic form by copying is an irrelevent implementation detail. The tech is there to transfer ownership, we are simply denied it by license.
And then the lending provisions. You could lend your kindle to someone (giving them all your books rather than just one). With a paper book you can give the book away or lend it to people in a serial fashion for however long you want. The tech is clearly there (single, two week lends) but the terms under which it operates are far more restrictive than a paper book.
--edit-- I realise that I first said ebooks and now am referring almost exclusively to amazon. It's entirely possible that other schemes could allow transfer of ownership relatively easily. I'm not aware of any that do right now, but there you are.
You own the paper book. The words are protected by copyright, sure, but that's not the same as the restrictive lease that ebooks are subject to. Very different beast.