He was handed hundreds of millions of dollars in personal wealth (probably either blackmailed or proceeds from money laundering or both) and decades of legal impunity to indulge his predatory urges. Up until the end he probably thought he was untouchable, or he wouldn't have flown back from Paris to be arrested at Teterboro airport in the first place. It's not hard to understand why he took this "bargain." I'm sure the intelligence agencies who helped set it up even put some twisted "it's your patriotic duty" spin on it.