Federal habeas corpus for state prisoners only exists because Congress created jurisdiction for it. Congress expressed its judgment that the actual merits of the case are best addressed by state courts for prudential and constitutional reasons (subject to limited exceptions). In this case, the guy pushed a claim on habeas that was clearly not presented to the state court.
Federal judges do not have the power to invoke jurisdiction where it hasn't been granted by Congress or the Constitution. This is a bedrock principle of constitutional law since the founding.
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