Because there is no universally agreed list of countries. For example, this article answers the question "How many countries are there?" in 6 different ways, producing 5 different numbers.
Maybe, but personally, I think that China is nowhere near the bottom of the happiness index, and likewise, the United States is nowhere near the top. However, it is without a doubt that North Korea must be one of the least happy nations in this world.
They are happy to be Korean, and happy to have plenty of kimchi, and happy to be so close to the dear leader... but sad that the evil American Empire has forced them to cut off ties to their rightful masters to the north; but check out the rankings it skips from 5th place to 152nd.
but no taiwan or kosovo
However, quite hilarious.