I can't answer your last two questions, but I can speculate on the first
one. (Then again, perhaps a real book store, such as "Barnes and
Noble", has such a feature -- I don't know.)
My guess would be that when Amazon branched out from being an on-line
book store, into a nation-wide behemouth, at some point along the way,
they decided that they no longer need to cater to small end-users who
are going to Amazon to buy books. I'd assume that book-only buyers make
up a *very* tiny fraction of Amazon's sales, now. I wish that they
stayed a book-store only.