Correlation vs causation.

You assume that the 4.9 time spike at the end of the year is due to managers frivolously wasting their budgets to pad it out. And I have no doubt that some do this.

But there is also an equally plausible and much more rational explanation that would also explain the spike in spending at the end of the year.
The department has some low priority spending goals that their employees identified during the year, maybe things like upgrading keyboards, or even starting a new project that would be beneficial but is just low priority. Management does not know exactly how the year will go, so they delay committing to these things as long as possible, so that they have some money in case of an emergency. But as the deadline of the fiscal year approaches, they can get more confident that they can spend this money on the lower priority things, and not expose themselves to a risk of IL-liquidity in their budget, because it will be refreshed soon.