GDP can be one marker for 'things are improving'. Of course it isn't the full picture - when you are living in increasingly restrictive state monitoring you against your own will, you feel the government is bunch of idiots, jobs have been shifting away and so on and on, people are not that happy. Rich are getting richer, poor poorer. If you are 2 joints away from serving prison sentence and having your life ruined for good (maybe less relevant these days).
Losing 'friends' around the world - 30 years ago, americans were heroes, WW2 saviors of the europe and the world, America was land of endless opportunities and most importantly - freedom. Now its the opposite - unlawful killing of somebody with tons of civilians with drones wherever they want, and in the same time being very friendly with horrible regimes like the one in Saudi Arabia because oil and money. Freedom and US ain't the same thing after 9/11.
Plus on top of that workaholic US mindset, that weird attitude that your job defines who you are and whats your position in society. None of this can make masses happy, in contrary.