Every system that works has a recognizable rhythm. In government contracting that rhythm is annual – the season in this industry starts in October when the fiscal year begins (important only for accounting and taxes).
Some officials like spending during the year without much of the remaining budget in final weeks. Many other officials allow for significant delays in major spending throughout most of the year or a litany of other reasons that prevented them from exhausting their budgets for agreed upon projects.
If the budget is sent back to the Treasury with a surplus, they will get less for new potential projects coming down the pipeline in the following seasons. Even if there were disagreements throughout the year on projects, they must spend the budget or less is given in the future.
Differences in spending styles have shut down Congress several times…not perfect but there is a recognized season – largely determined due to taxes and such – that is a beautiful autumn cascade of job contracts for the willing and qualified leaders of America.