It is extremely clear why when you look at the outlays. [1]
75%+ of revenue is spent on welfare of various kinds.
Welfare is typically ment to mean policies to alleviate the hardships of poverty. These can be wealth transfers or socialized insurance policies to reduce the variability of outcomes.
Public goods are services like roads, courts, or firemen.
Compulsory and universal participation are the methods used to achieve this goal.