There isn't just one Government in the US. What we have is a system of branches, each of which must agree that a law is acceptable. If just one branch disagrees then it can effect change.
Similarly we are not just one state. We're a federation and individual states can fight against federal laws that their constituents find unjust. Washington and Colorado did just that when they legalized marijuana. It's still illegal at the federal level, but the ATF has no jurisdiction within state lines so they can't do anything about manufacture and sale within state borders.
Consolidating that all under the same umbrella erases a lot of the very complexity that serves to protect you. And you can't accord that complexity to a corporation because shareholders and the board have a level of tyranny not found in our government.