I'm not sure if there is a "law" around this, but, I assume nearly all contracts go over budget. Private or .gov.
But, government contracts are pretty beholden to a tight, static budget. Once the money is gone, it's gone. You can't necessarily go ask for additional taxes and budget for the year. Many times, you literally cannot go over budget no matter what. The pay-as-you go, variable pricing you get in the cloud, is actually a challenge in government budget.
In the private sector, when you go over budget..funds can be found elsewhere in the company, etc.
But, government contracts are pretty beholden to a tight, static budget. Once the money is gone, it's gone. You can't necessarily go ask for additional taxes and budget for the year. Many times, you literally cannot go over budget no matter what. The pay-as-you go, variable pricing you get in the cloud, is actually a challenge in government budget.
In the private sector, when you go over budget..funds can be found elsewhere in the company, etc.