Interesting. Thanks Richard. I (and I suspect many) do the same with pbooks, purchase and either never get to or get to much later.
Too many books, too little time.
It does have to do with marketing and tastes certainly. And certainly if something is offered for free it may get downloaded but not read for a variety or reasons including tastes and interests and the depth of the TBR pile.
On the other hand what is 'lost' by the author giving the book away under those conditions is possible future sales. If a reader enjoys the free book they are likely to purchase other books from the author. After all that's the main point of given them away in order to sell books. If one just wants to give their work away then that is a different situation.
Interesting about your bias against Amazon exclusives. Do you hold the same views for the print publishers? For B&N Exclusives? Baen Only books?