IMHO the top ten countries on World Happiness Report are primarily those that are good at expectation management. The Nordic countries always rank well because culturally they manage their citizens expectations in life so as not to expect too much (cf The Jante Law). Australia and New Zealand have similar cultural drives where being too successful is seen as a negative. The US does not - if anything, US culture is the polar opposite of expectation management.

When walking through the CPH airport with one of my Danish colleagues, they would always roll their eyes at the "Welcome to the happiest country on Earth signs" and point out that Denmark was ranked #1 in SSRI use in Europe.