Motorola has been through a pretty interesting few years, with Google buying them in 2011 for $12.5 billion then sold it to Lenovo in 2014 for $2.9 billion. Google didn't public state that they sold Motorola because they were getting negative feedback from their hardware partners over possible preferential treatment towards Motorola, but many feel that's the reason. Google sold Motorola to Lenovo in 2014, but kept the patents (hence why the price was a huge difference). Also in 2014, Motorola built the Nexus 6. Which is still the largest Nexus smartphone to date.
It's said that the Nexus 6 by Motorola was "thrown together" at the last minute. And that's a big reason why the device looks a lot like the Moto X 2014 that Motorola released about 6 weeks earlier. The Nexus 6 had a 5.96-inch display, that's a huge display, especially with front-facing speakers. Many reviewers were not to happy with the size, and that shouldn't be a surprise. According to Motorola's Chief Marketing Officer, Adrienne Hayes, Google wanted this screen size. She also noted that they could have built it with the same display size as the Moto X.
Hayes also notes that "you learn as you go...this time period that we were jumping screen sizes so quickly. I think it was one of those where we were like 'is it [screen size] going to continue to go up?' I think unfortunately, that was one of the products that was going to be the example of no, it's not."
She's right actually. Since the Motorola Nexus 6 came out in the end of 2014, we've started seeing a shift towards smaller smartphones again. The Nexus 6P is a bit smaller at 5.7-inches, the LG G5 actually shrunk a bit to 5.3-inches and even Sony's own Xperia X Performance that was announced this week has a 5-inch display when their Xperia Z5 had a 5.2-inch display. It's unfortunate that Motorola's Nexus 6 had to be the guinea pig to show everyone that screen sizes won't continue to grow, but at least we know now. While the Nexus 6's screen size was pretty large, there were still a good number of people that enjoyed that large of a display, even though it was definitely a two-handed smartphone. It also made Google think about the 2015 Nexus cycle, and bring them to the epiphany of creating two smartphones, one that's a bit smaller and one that's more of a phablet sized device.