I don't really think this is valid reasoning tbh. Governments can kill people at a whim, but frequently do not because they would rather they die over time through conditions such as prisons. There are other factors they consider apart from simply wanting him dead. They don't need to have killed his directly. It could simply be the result of mental and physical health issues due to his imprisonment. Life expectancy in prisons is markedly lower for a reason.
I've seen takes that he was killed by the West to blame Putin, but I haven't really seen any actual hard evidence for this
Western governments want Assange dead. So by that logic he'd be dead long before now. He's not, but I'm not about to conclude that the US gov doesn't want Assange in an anonymous ditch. There are plenty of revolutionaries being let to rot in US prisons from the previous decades. It's just killing them in slow motion.
At the end of the day we don't have objective info to allow us to conclude one way or another as to exactly why he's dead, and both the West and Russia are obviously deeply biased sources.
Yeah it's also crazy when you realize instinctual it is. Like I don't think all the dolts at the Guardian pumping out ink for the ink god really reflectively think 'we have to craft this manichean narrative for the sake of liberalism' given that's not actually how ideology generally works. I have no doubt (actually, I know from personal experience) that it you push narrative which don't conform you will sometimes get responses which straight-up make no reference to the truth of the matter but explicitly reject what youre saying because its politically inconvenient. That being said, it is fascinating and disturbing of reflexive and instinctual these kinds of responses are in general culture, and how little most people in liberal societies are either willing or capable of critically analyzing and evaluating this kind of stuff. Like they could just read what Putin says to get a more accurate account of the Russian state's motivations for their actions.