It bends because an area on the Iphone 6 doesn't have as much structural integreity compared to previous generations. If you apply enough pressure with your hands, you can make the Iphone 6 bend. This isn't a good thing because if you apply enough pressure, you could damage or break your device entirely.
That being said, other smart phones are capable of being bent as well, but the amount of physical force needed is greater than the IPhone 6's.
I'd recommend that you don't try to bend it out of curiousity and just understand that it has a structural flaw in this regard and you should be careful about it.
