To quote the end of the article:
what exactly is the motivation behind making larger smartphones instead of smaller ones? Jaycox said the tablet and smartphone markets are going through a test phase as consumers search for the sweet spot, looking for a portable device that meets all their computing needs.Translation: We don't know what to make so we are throwing everything we can against the wall. Let's see what sticks.
"What's that device size where people truly feel like they have an all-in-one?" he said.