1. The Mueller report presents uncomfortable yet legal, coordination with WikiLeaks, in which case extraditing and prosecuting Assange would allow administration to distance itself and present any coordination as incidental.
2. Assange releases were cited in FISA requests. If intelligence agencies had an established assessment on Assange's ties to Russia, and requests were authorized with elements contradicting those assessments, it could raise eyebrows. It seems firmly establishing presence or lack of Russian backing, along with sources would bring clarity to several matters.