I think that's actually the effect of anti-trust/anti-monopoly laws.

There's a point where companies get "too big to fail"/"too big to jail" and have outsize effect on the country (especially if the country is stupid enough to pass a Citizens United law that explicitly allows them to do this). Anti-trust laws are the main way that the government tries to prevent this, and haven't really been used since Reaganomics decided that big == efficient. Until recently.

Passing a law that companies cannot exceed a certain size (market cap as a percentage of GDP, I guess?) would probably be a simpler way of achieving this. Though, obviously, the accounting profession would roll up its collective sleeves and declare "challenge accepted".