Happiness being subjective to cultural differences is a feature, not a bug.

If a culture is breeding widespread unhappiness (perhaps in exchange for maximization of economic growth over all) then it's something that should be observed.

Do you think people are lying about their happiness or that happiness isn't subjective?

Self-reported happiness (or life satisfaction) is only a part of the ranking. The objective measures correlate strongly with the subjective ones (with some outliers like Israel). But as any metric, it's of course not perfect.

"Happiness is measured using six categories including GDP per capita, social support, and healthy life expectancy, among others."