In the OP, some small fish were colluding. The only unregulated monopolies I can think of (Google search, Apple App Store, Monsanto, Boeing) are very large and powerful, and they'll certainly have many national politicians in their pockets.
So I don't find it odd that large monopolies aren't busted very often. It's a predictable outcome of a money-driven political system.
Patents are an example of government granted monopolies (on an idea). The government also grants monopolies to certains businesses or organizations [1]. Government is itself a monopoly of sorts (they don't offer or allow you a choice in Law Enforcement provider).
Boeing may be a domestic Monopoly, but only because the size, scope and IP of the organization is hard to replicate. What would have been illegal if they had colluded with Communication Sat providers or NASA to prevent Musk from starting SpaceX. There is no evidence I can see that would prevent a sufficiently motivated entrepreneur from competing with them in the Aerospace Defense sector. Politicians are equal opportunity providers, they accept brides (donations) from anyone with a big wallet ;)
[0] http://en.wikipedia.org/wiki/Restraint_of_trade
[1] http://en.wikipedia.org/wiki/United_States_Postal_Service
Tee hee.
But, seriously:
> [Government doesn't] offer or allow you a choice in Law Enforcement provider.
The rise in private security firms and private offender-rehabilitation firms [0] kinda act as defacto law enforcement for some of the lower class.
[0] http://www.slate.com/articles/news_and_politics/crime/2015/0...
That sounds like a description of a somewhat sane legal system, but it's not a description of United States "antitrust" law. See, for instance, United Staes v. Alcoa.