They almost did in the early 00s, but unfortunately their lawyers were just as good then and republicans controlled the justice department.

For capitalism to work long-term there needs to be regulations (this was even included in Smith's "The Wealth of Nations"). But in the US people are incredibly hostile to any form of government actions, hence unfettered capitalism will continue and corporations will steadily grow into monopolies.

capitalism -> competition

Consolidation and abuse of capital to influence governing bodies, is the result of true capitalism (and almost any other system, ironically).