Statistical question

The importance of income inequality for public, politics, and economy is high. There are many surveys and estimation programs to measure incomes and inequality, including the level of poverty. There is no one complete income survey, however. Figures 1 and 2 show the shares of GDP and total population covered by major statistical agencies: the Census Bureau, the IRS, and the Bureau of Economic Analysis. No one is complete.
Why so? Why to have many incomplete data sets instead of one complete?
Looks incompetent.

Figure 1. Shares of personal income estimated by the CB (MI – money income), IRS, and BEA.

Figure 2. Shares of population reporting income covered by the CB and IRS.