(Why should I care what happens to other people, and try to avoid harming them? Because they're clearly conscious, capable of joy, suffering, etc. What about other animals, like dogs and cows and chickens? That seems pretty obvious too, given our biological and behavioral similarities. What about molluscs? Hmm, there are some potentially important differences there. What about rocks? I can't know, but they have none of the features I usually associate with consciousness, and if they do have internal experience I have no idea what determines it, so I might as well continue to assume not.)
As soon as you define consciousness in functional terms, you make it tractable, but you also detach it from the thing we were originally wondering about. (The problem is that purely materialist or functionalist explanations always run into the question 'but why does there have to be internal subjective experience associated with these things/events/systems, and not others?'. Consciousness itself, in the 'qualia' sense, never plays a functional role in these explanations -- and if we weren't already assuming its existence, they would give us no hint that it exists.)
I lean on defining the concept based on adaptation to the environment - consciousness is the function that adapts an agent to its environment. Its purpose is to safeguard the agent against external perturbations and achieve its own goals.
For example, how would we get food without consciousness. How would reproduction work? Consciousness has a vital role here. Evolution works at a slow pace, consciousness is required for quick adaptation, otherwise the penalty is death.
I think consciousness is being made into something transcendent, or unfalsifiable, or essentially different than physical processes because we like to make ourselves feel special in comparison to the world.