> Why would a government so keen on accusing people of espionage and no doubt wanting to set a precedent for various things being classified as espionage (such as leaks), settle so easily?

Because you've misunderstood the motive: it's not about setting precedent, it's about securing convictions for the people charged. Which plea bargain guilty pleas do.

> Daniel Ellsberg of the "Pentagon Papers" fame has made it extremely difficult if not downright impossible for the government to win in such cases.

For cases like the Ellsberg case , sure, but that's because of the gross prosecutorial misconduct in that case, not the substance of the charges.