Normal ontological reductionism doesn't work
In explanations of consciousness, the subjective, first person components can't be reduced away as nothing but physiological activity, because then the essential feature of consciousness will be left out.
This is unlike many other scientific's explanations, in which the subjective component can be (ontologically) reduced away as unimportant.
For example, in physical explanations of the nature of colour, the colour experiences ignored in favour of a claim about photon emission of certain wavelengths.
But in consciousness the appearance is the reality.
John Searle (1992).