The 787 is a wonderful jet. It sips fuel, flies fast, goes really, really far. Guys who fly it love it.
As fuel costs increase, and they will, airplanes like the 787 and the 737 Max give operators a big fuel cost advantage.
For comparison, the 787-8 has roughly the cabin size of a 767-300.
But it flies at 0.85 vs. 0.82 of the 763. It burns about 60% of the fuel. It has much greater range.
On long flights, that speed and fuel burn are a huge advantage. The range offers new possibilities and new markets.
When going to smaller markets, a medium size airplane that can offer direct service (e.g. SFO to Chengdu) is a huge time savings for customers who would otherwise have to connect in a major hub (e.g. Tokyo, or HKG in my above example).