Having worked in a federal agency one experience is that they never fail to spend all of their money they are given. Rather than indicate that they have not spent it all and return it to the Treasury they set up end of the year projects to ensure that All is spent. They do this out of the fear of NOT getting money for the next year. Most of these end of the year expenditures are BS! Plus salaries are always being raised.
No matter how it’s done, cutbacks in spending result in economic recession, which is anathema to voters, and hence to politicians. So it can’t happen until the apocalypse. .