It's likely the same reason that most businesses are willing to pay for software: service and support, as well as many vendors likely being willing to implement

It's likely the same reason that most businesses are willing to pay for software: service and support, as well as many vendors likely being willing to implement custom features. On top of that, none of those agencies are likely to be willing to download some pirated crack for whatever piece of software they need, so that means if they want it for free they have to crack it themselves. Which requires them to divert people who could otherwise be doing things that are actually relevant to their missions. There is plenty of funding in these agencies to buy software and there's little to be gained from stealing it.