This is very much on purpose. Capital is extremely mobile and not part of a market transaction, while most labor is immobile and constrained as a market transaction.
It is easy to take tax from a labor market transaction, and this tax is borne just as much by the capital employing the labor as by the labor itself. Taking tax from capital appreciation is far more difficult - if you put your capital tax too high, the capital just moves to a different market with better dynamics.
Of course if you go overboard with your labor regulation and tax, then other labor markets are able to out compete your own labor market, and that is even worse.
Basically: you don't have free reign to decide on these labor and capital taxes and regulations. Any policy change you make is going to have consequences. You can't just say "OK, we will just double capital tax! Money for all!" and not face extreme changes in your entire base.
I'm in South Africa and watching this unfold as the socialist government continues to raise capital taxes each year, and now faces enormous foreign capital flight and lack of investment in the economy, destroying GDP growth and pushing the more vulnerable parts of the population out of jobs and into extreme debt and poverty. Believe me, you don't want that in USA just to get rid of some mythical '1% problem' that hurts your sensitivities.