Corporations have a far more limited scope.
Even if you are all a bunch of damn cynics
the government is interested in holding its territory, protecting its infrastructure and resources, population, keeping order, etc.
Corporations are interested in making their stock go up. Not even long term growth, just the next quarter. They'd disband the entire company if sufficient stock gains would occur.
Governments don't get that option. Their existence in a physical rather than purely monetary world prevents it.
(yes, I know corps are composed of people and resources, but only as a means to a monetary end.)
To have a truly feudal corporate system, ie cyberpunk novels, you'd have to have corporations that were more interested in power, or at least _very_ long term profit, than in what the stock market was doing.
In other words, they'd have to want to govern.
Japan is a case of its own, because government there did/does feed and control the corporations. You could call it corporations controlling government (you'd be wrong, but whatever) or government controlling corporations (pretty much true) but either way the corporations are interested in serving the interests of Japan as a nation even if it means undercutting their own profits.