Why do they need so much ammo?
First, they aren’t actually being delivered that much ammo, they are contracts to lock in the price for ‘up to’ that much. We don’t know how much they are actually buying within that contract.
Second, they have needed ‘that much’ for a long time, at least since 2001 they have been purchasing at least 230 million rounds per year. (and if you do the numbers, you’ll see the current half-decade contracts versus annual then are about the same total amounts).
Homeland Security is the umbrella that covers agencies like ICE, Border Patrols, Customs, FBI, etc. All of those agencies burn millions upon millions of millions of rounds at practice ranges alone. Who knows how many are also being stockpiled anticipating future shortages, etc.
My point is that people are making a big deal out of something that isn’t that much out of the norm. The libs screamed about Bush using these on them when he was President, now the roles are switched. This is a usual storyline that switches players as the PTBs switch.
Who knows, maybe they are planning for another civil war.
[Why do they need so much ammo?]
Because many of them are lousy marksmen.