Erm, because the Swedes wouldn't agree to guarantee him that they wouldn't extradite him to the US? Of course, the charges were so weak they could have just been dropped. Or they could have sent someone to the UK years ago. Or they could sort out their absurd sexual assault laws in the first place.
There were many relatively easy outcomes, none of which happened as far as I can tell, because of the stupidity or stubbornness of the Swedish authorities.