I am guessing Finland and other Nordic countries are coming out as the happiest nations on earth as standards of living are fairly high, you have great social net and vacation time.
USA has a lot more competitive pressures and financial stress due to lack of a social safety net and a workaholic culture where there is pressure to show up at work even if you are exceeding your vacation carryover limit for the year and effectively not even taking the two weeks a year you are allowed to take...