From my understanding at least some of that may be due to the way annual budgets are done, unless it's changed in the last decade or so. In short, if a group didn't spend most/all of its budget, it would be reduced. One of my old roommates enlisted after college and worked in a USAF group's purchasing department, besides his main duties. He told me about the times they scrambled to find something they could buy near the end of a quarter or fiscal year. They had to have some justification for the new stuff, however, so they couldn't keep replacing the same things, so one time it may be tools, then instruments, then electronics, etc. So I'm going to guess that, for someone, one year it was toolboxes. But this is all a guess based on now fairly dated second-hand information.