Because it was a bet either way. Indeed your stalemate. After this there might have been other legal avenues that the US would have attempted… prolonging the whole ordeal.
Especially the human aspect. Government employees just go home at the end of their day and sleep fine. Assange spent his time in an embassy/prison while this whole ordeal went through. Now it is over.
The US did not have him in one of their actual prisons, but they did imprison him for over a decade.