...Because it can break sooner than you'd expect.
I question the very reliability of recent phones, phablets and whatnot. It almost seems that companies like Samsung purposely try to put those phones in plastic casing; as if they just want to cash in on shorter life expectancy of their products. I recently got a new "phablet" phone, I guess. It's a Samsung Galaxy Note 3 Neo. I even made sure that it would get good, durable casing so that when it falls short distances it wouldn't shatter like glass. One day I had it in the backpack, and I do handle backpacks with certain care as I always carry some fragile stuff in there. I don't know if it was because of the cold winter or it bumped against something flat, but after returning home and pulling the phone out, I noticed that it suddenly had this single, ugly crack going all across the phone, smack dab in the middle. To be honest, it's not really that noticeable when I face the screen up straight, but any other angle reveals that one crack.
This infuriated me, even though it didn't really affect the performance that much. I don't really know what caused the crack, but I did certainly learn a lesson: Don't buy phones greater than 5 inches in diameter because not only can they turn out to be more fragile, they might just become an easier target for theft. They're pretty unwieldy and unfit for travels.
I'm going back to using my Galaxy S2 when on the go, I guess.