The charges the US attempted to extradite him for were based primarily on things he did or allegedly did or which came to light after the rape charges.
Ockham's razor also applies. If you want Assange charged in the US on 'espionage' or similar and you have a choice of notifying the Swedish authorities that he is wanted for serious crimes in the US or instead relying upon separate local allegations that are so vague the Swedish legal system has to work its way through an appeals process to even decide to whether to pursue the case or not whilst leaving him at liberty to leave the country, you're unlikely to choose the latter.
Ockham's razor also applies. If you want Assange charged in the US on 'espionage' or similar and you have a choice of notifying the Swedish authorities that he is wanted for serious crimes in the US or instead relying upon separate local allegations that are so vague the Swedish legal system has to work its way through an appeals process to even decide to whether to pursue the case or not whilst leaving him at liberty to leave the country, you're unlikely to choose the latter.