The motivation of the giver is definitely one issue. I can see the Fire being bought as a cheaper alternative to an iPad, or being given to a child to encourage them to read.

The cost of ebooks is another issue. Almost everyone that I talk to is shocked to learn that ebooks as much as (or more) than paperbacks.

Technical knowledge is yet another sticky point. It may be dead simple to buy stuff from the vendor's book store, but getting free stuff requires a bit of background knowledge. (Examples: how to search for free books in the vendor's book store, knowing about places like Project Gutenberg or Archive.org, understanding the different ebook formats.)

Oh yes, and you aren't necessarily going to toss away your current pile of to-read books to dig into ereading.