To me it is pretty ridiculous how much labor is taxed, and how little capital is taxed. Especially if we are worried about automation and lack of productivity growth, it seems so counter-intuitive that we are completely stuck to a tax system that devalues workers.
The reason is simple: labor has less options. Capital can mostly go where it pleases - if it is taxed too much it might flee the country. But your 160 million workers aren't going to uproot themselves and move to another country because they're too heavily taxed.
Sweden has a capital gains tax of 30%, two to three times that of America and they have a similar GDP per capita, depending on the year.