The fourth possibility - and this one never ceases to be true in all cases when it comes to the Feds - is that the people seeking his prosecution are spiteful as hell. They are not used to not getting their way. It's extremely fearsome to go up against the US Government when it wants your neck, because they have so many ways to destroy your life all around the world. They have infinite resources for all practical purposes and can just keep coming at you.
One of the few consistencies I've seen in my lifetime across all major US Government agencies is that they seem to hold grudges forever. It doesn't matter whether we're talking about the FBI, CIA, Pentagon, DOJ, IRS or SEC. Assange, out there, is a persistent waving defiance of their perceived power and reach (and worse, right in the US sphere of influence).
Supporting your point are people like Poitras getting extra, random screening after publishing documentaries about US wars. They've often been vindictive given it's power-loving, egotistical, image-conscious politicians running them.
+1. When I was a Boy Scout, I had confirmation direct from an FBI agent that once somebody is wanted, the Agency has a long memory and a long reach.
The anecdote he shared was a fugitive fled to Saudi Arabia. Over a decade and a half, the fugitive grew a small business empire and was well-connected. In tandem with allies in Saudi Arabia, the FBI arranged a lavish party on a yacht to which their target was invited. The yacht sailed out to international waters and FBI agents apprehended him and put him on a Navy cruiser out at sea.
One of the few consistencies I've seen in my lifetime across all major US Government agencies is that they seem to hold grudges forever. It doesn't matter whether we're talking about the FBI, CIA, Pentagon, DOJ, IRS or SEC. Assange, out there, is a persistent waving defiance of their perceived power and reach (and worse, right in the US sphere of influence).