1. Real keyboard. I carried the iPhone for 3 years and never liked the soft keyboard. Most of my usage is text entry (messaging and email), so being able to do this quickly and accurately matters. I much prefer text entry on the Passport, both because I find it easier and more accurate, and I don't give up half the screen to the soft keyboard.
2. Dev / unix tools. It might be a bit surprising, but the BB10 dev kit is actually pretty good: Several API options; no barriers to getting started (download and go); and you can access / expose / augment the unix userland underneath. With a command line app, it feels like a real computer. The keyboard makes this experience better.
Since switching, I have also been pleasantly surprised by the size and quality of the screen - 1440x1440 is kind of awesome (more pixels than my laptop). Blend has also been unexpectedly good.
Anyway, that's me and my reasons. I'm just a unix nerd in the consumer market. I'm not into flashing ROMs or jailbreaking or anything like that, and I find the BlackBerry keyboard lineup pretty compelling. YMMV.
Blackberry's current success comes from selling these people exactly what they want; an upgrade from their current model that is almost the same in form and function. When someone wants a different form and function they go to an iPhone or an Android.
You'll be seeing and hearing a lot more about Blackberry. I can assure you that.