I've posted in many threads explaining why I transitioned to a 6 from a Plus and it mostly involves the unwieldiness that comes with a device so large and tall. The screen, battery, and camera are awesome no doubt, but seeing as it's important I have a phone that's able to be portable and also function as a quick-action camera, it's important that I have it be more in the design of the 6.
I love the Plus a lot, I do. But after a few weeks with it, I started to notice things becoming a total hassle that were once easy for me. With older phones I had, taking pictures, sending texts, all of these I could master with one hand if necessary. The Plus dramatically changes how you approach the device, and it just seems unnecessarily big to me due to the bezels. It's just too hard to do anything that quick with the Plus once you step out into the "real world" away from the luxuries of home.
The weight is also a factor to consider, while the numbers might not seem that drastic, the iPhone 6 is like a feather by comparison. One of my favorite features of the iPhone 5 series was how light it was, and the Plus kind of went far away from that.
Basically, I loved what the Plus is good at, but I hated what it isn't good at. Almost any form of true, one-handed use is null and void.
I did get "used" to a lot of the Plus' mannerisms and quirks, but it just became too much of a hassle to operate one-handed (I do not think all phones have to be "one-handed"), it's just that the Plus doesn't have to be as big as it is in length, because other flagship Android phones are far smaller and happen to have a bigger screen.
I really need something that can be dimensional in the way I need it to be. Getting emergency calls, quick texts, very fast pictures of moving objects: all of this is easier on the smaller form factor. The iPhone 6 isn't small, it's about the same size as some major flagship phones, and until they trim the bezels and make it leaner in the body, the screen size shouldn't get too much bigger.
I was once in the "I'll never go back to a smaller size!" group, but after numerous, fumbling attempts to dig for my phone while seated, and many moments trying to capture a picture or video and dealing with the unorthodox size that cramped my pockets just was too much to sacrifice for the extra inch of screen real estate.
Hopefully by the iPhone 7, Apple will make it lighter and make the phone less-long in the hand so that it could be an actual revolutionary phone. I mean, it's awesome as it is, but it's more of a tablet ("phablet") and I need something that I can operate in any situation and the Plus is just too difficult to accomplish that (unless you have massive hands). And yes, hopefully it won't bend as easily.