The truly big ticket items are extremely unpopular among most voters: cuts in social security, Medicare, and huge tax increases on certain groups of people (the most influential folks). Also, a huge simplification is that we ignore the impact on the economy; one of the central arguments for keeping the tax cuts is that it supposedly creates more jobs, as does government workers and aid to states.
Very cool find, though. Maybe it should be a required exercise before each election season, just to discourage politicians from focusing on the less important topics.
One last eye-opener: this only helps plug up the year-to-year budget deficit. The actual national debt is $13.5 trillion, and should another recession hit us between now and 2030, we'll be in bigger trouble even if you managed to balance the budget in this "simulation."