Space, the final frontier (more like the "limited frontier" because I don't have room for pbooks in my condo... I have a bunch in storage).
I decided a couple of years ago I wanted to get back into reading and having ready access to just about anything I want to read in seconds makes it easy.
My aching back (less weight in my purse or backpack).
For me ebooks are cheaper because I buy mostly new fiction releases. I prefer to buy books as I'm not much of a library person (though I'm giving it a try right now but the wait lists are crazy long).
I just like gadgets.