Within one year, the screen size of nearly all mass-market smartphones took a huge bump from 5.x" to 6.5", because of two ODMs (device manufacturers who are contracted by big brands to design and produce smartphones). Those two ODMs won contracts to produce mass-market devices for the brands Lenovo/Motorola, Huawei and Xiaomi based on a 6.5" 720p LCD.
The total volume forecast was so big, that suddenly 6.5" displays were cheaper than any other 720p smartphone panel. Other Smartphone brands adjusted mid-development because the larger panel also made the PCBs and batteries cheaper. In that year, mass-market devices with 1080p displays were often smaller (which was contradictory for a vendor-portfolio until then) because there was no such economics of scale on higher-resolution panels.
So within a single year, displays got a full inch larger, not because the consumer demanded it but because of supply-chain dynamics.