doing?
The rich are using very efficient assets (at least using recency bias, time will tell) to leverage and gather more resources to do whatever it is they want, whether more investment, or lifestyle or whatever. The reason they can do this is because there is such massive difference between interest rates and expected rate of return for their investment (mostly stocks).
The federal government is doing the exact same thing, except instead of a stock or set of investments, the federal government (and the fed for that matter) is using the American consumer as the collateral to lever up like crazy to do whatever it is they want, whether it be infrastructure (arguable what that word means these days), or just handouts (aka lifestyle). The reason they can do this is because the world will buy the debt up like crazy while the American consumer is expected to continue to be the most predictable place of growth.
The taxes are a big part of this, but interest rates being nothing are even more important to this whole equation.