> To the extent that a law not prosecuted is a law that doesn't exist, you're correct, however I've provided the statutory citation which states that "every" contract, etc., in restraint of trade, "is declared to be illegal".

Laws are not interpreted de novo, to mean whatever you think they mean. In our common-law system, laws are interpreted by the courts, over a long period of jurisprudence. In the case of the Sherman Act, we have over a hundred years of case history to guide us.

The courts say that it must be an "unreasonable" restraint of trade. After all, every contract is a restraint of trade! If a grocery store signs a contract with a farm to buy all of their lettuce, then the grocery store isn't going to the central produce market, where everyone has a chance to compete. If Apple signs an agreement with Samsung to source its ARM CPUs, that means that Nvidia doesn't get a chance to compete for the duration of the contract.

But that's completely ridiculous, right? They got the chance to compete for the contract. And that's exactly why it's not an antitrust violation. It's a restraint of trade, but it's very much reasonable.

Note that the word "unreasonable" doesn't actually appear in the Sherman Act. It just says "restraint of trade." The Courts added this test because they felt it would be counterproductive to interpret the Sherman Act literally. As you're doing.