The same reason condo owners can't sue their own board. The owners elected the fools, and the compensation would come out of their collective pockets. You are all in the same boat together, and the government and it's court systems, work as a whole. The only way to hold an entire government accountable is to go to the world court, and even then they won't hear individual cases of abuse.
Now...corporations are legal entities and SURE you can sue.