I think we already know the answer. We need to go further and try and understand what this partially veiled, but completely serious, US and UK destruction of a modern journalist means for all of us.
Assange is an advocate for whistleblowers, a promoter of information access and information security for everyone, not just governments and major government-connected corporations. He, with the help of information security specialists, codewriters, truthtellers and witnesses around the world, received and published material that embarrassed and exposed a number of powerful organizations, including the US government and its many cronies and beneficiaries.
Why is he being tortured to death? Why is he still being subjected to new and experimental variants of BZ fresh from Porton Down, and deprived, not only of friends, relatives, and unsupervised access to his legal team, but to food and basic care?
The short answer is that he is being held on behalf of the United States and he is being chemically and physically interrogated in Belmarsh (the British Gitmo) in order to reveal his private cryptographic keys, and the names and cryptographic information relating to others within the Wikileaks information network. The arrest of Ola Bini in April with new charges filed last month, and the re-arrest and incarceration of Chelsea Manning, speak to part of the effort to find the anonymous leakers of information from the NSA vaults, specifically their hacking tools cache leaked in 2016. This is generally indicated but not completely put forth in the US indictment.