You are not wrong. Nor are they.

Some of the Bernie people managed to sneak their way into the Biden administration in a few minor departments.

They were too virtuous to run an election but they seem to make pretty decent policy decisions

Or: nothing really interesting happened here at all, the USAO figured they were 2-3 years out from wrapping up a trial on these charges, that the only toothy charges they had for Assange were conspiracy charges for which Assange's active participation was weak, and so the sentencing guidelines would likely have left him at "time served", which is not a good use of the prosecution's time.

But, I mean, sure, maybe Biden directed DOJ about an open case, and AG Garland just rolled with it, because he sure seems like the type.