Why do AI researchers seem to think that consciousness is a computation?
Consciousness as a computation is not by any means a scientific fact.  Firstly because there's no universally accepted definition of consciousness.
General AI does not have either a widely accepted definition.  There are two hypothesis in relation to consciousness: Weak AI states that you can achieve AGI with the computational models that we know e.g. without &quot;consciousness.&quot; Strong AI, on the other hand states that there's something beyond our known computational models that is needed to achieve AGI.
Neural networks as used in machine learning are modeled in biological nervous systems but I don't think anyone has claimed that consciousness or even AGI can be expected from their implementation.
Some proposed consciousness theories worth mentioning are:
Daniel Benett's: Consciousness is nothing special. It's an illusion that you have control of your own decisions.  He backs it up with some experiments that have been done where subjects think they have reached a given decision.  In the experimental setup, however, it's demonstrated that before the subjects confirm that they've taken their decision an external observer can already determine the decision that the subject will take.
Douglas Hofstadter's theory of consciousness is based on the idea that consciousness is an effect achieved through computational deep recursion.
However, as I mentioned in my first point, consciousness is not scientifically defined to be even possible to set up a proper experiment that could determine wether consciousness can be achieved through computation or not.