On the BBC website regarding this story it says "Police from the UK, US, Germany, Sweden, Portugal and Romania were all involved in the dismantling of the online platform." Which shows what he was doing was obviously illegal in all of those jurisdictions.
Since he was arrested in the UK and is a Portuguese citizen I don't see what is the reason he has to be extradited to the US and can't be deported to Portugal to face charges there or tried in the UK?
Also on the BBC "Special agent Jason Kane, from the US Secret Service, said: "This global investigation signifies the remarkable dedication of the US Secret Service and highlights our partnerships with our foreign law enforcement counterparts essential to disrupting sophisticated networks of cyber-criminals."
I thought the secret service job was protecting the US president not going after people selling stolen credit card details?