According to Wikipedia from October 1 to October 17, 2013, the United States federal government entered a shutdown:
(..) curtailed most routine operations because neither legislation appropriating funds for fiscal year 2014 nor a continuing resolution for the interim authorization of appropriations for fiscal year 2014 was enacted in time. Regular government operations resumed October 17 after an interim appropriations bill was signed into law.
During the shutdown, approximately 800,000 federal employees were indefinitely furloughed (..)
The reasons are quite clear, but I am wondering why does the law allow such an event as it seems to generate very undesirable effects? Why not temporarily function using previous year approvals (some sort of extrapolation) until the appropriate legislation is approved?
Question: Why is the US federal government allowed to shutdown?