Programs can be engorged with money one year and fall off priority lists the next. The Assistance to Firefighters Grant Program/Fire Prevention and Safety Grants demonstrates this better than almost any other, as it had more than $500,000,000 available in 2006—and this year it has all of $2,750,000 (warning: .pdf link). In other words, the Department of Homeland Security, or Congress, or someone, ran out of money for or interest in firefighters.
This absurdly abrupt change in funding also demonstrates why you should apply for attractive funding opportunities as soon as you see them because they might be gutted next year. While old programs are seldom outright eliminated, it’s not unusual for zombie funding sources to keep lurching about without real funding. Occasionally they’ll spring back to life with an infusion of cash, but this is unusual without some impetus.