If you reduce all x to nothing but y, then what you have left at the end of the process is no x at all: nothing to explain. To say that x is nothing but y is to say that there is really no such thing as x in the first place.
Eliminative reductionists generally prefer to overlook this difficulty. They try to explain explananda exhaustively as nothing but collisions of dead items, yet retain their reference to the explananda. They won’t take the last entailed step of asserting that there is in the first place simply no such thing as the explananda.
They can’t. If improper reduction is to proceed – if these reductionist guys are to have jobs – it must have something to operate upon. To say simply, e.g., “there is no such thing as consciousness,” is just silly, is risible. Nobody would pay to hear such a stupid statement. People want to understand the consciousness that is the warp of all their lives, not hear that it does not exist in the first place. Much better then to say that consciousness is a configuration of particles or a condition of fields or something, because to all but the most alert readers it does not have the effect of deleting consciousness from reality altogether, and with it the very reason of the investigations of reductionist cognitive scientists.
The bottom line is that when reductionists say that x is nothing but y, they cannot really mean it. Nor do they, in fact. They still talk about consciousness as if it is real, ergo available for explanation. How not? You can’t assert that you yourself do not really exist, for what does not exist can have no property or capacity of any kind, including the capacity to assert that it does not exist.