The electronics market is highly competitive. It is all about what the consumer wants and who can give it to them first. When Apple sees success in Droid phones, they have to compete as best as they can. The Galaxy Note, the Galaxy S5, and the Windows phones all came out with more user friendly, enlarged screens recently. When people began to turn to these brands over Apple, they had to come up with a product that could compete.
I was told that the larger screens are because of battery demands. In other words, to keep up with all these devices need to do, larger batteries are needed to power them, so the larger screen is the positive spin they put on it. Most people I've met who have used smart phones with larger screens complain that it isn't convenient to carry around in their pocket.