WHY has there been a reduction in governmental powers (in postmodernity) ?

As the corporations have gone multinational, they have gradually acquired greater power beyond what was originally granted to them by government, and have overshadowed the role of government throughout the world, essentially running things behind the scenes by bribery and coercion. The world needs to get a grip on this and band together to scale back the power of corporations before there's literally nothing that can be done about it. It's not too late yet.