>>16783422
We don't have enough information to empirically answer that question or several other questions that would need to be answered before we even approach it (see: solipsism).

That said, let's make the following assumptions to give this question as much "meaning" as possible:
>all biological organisms that appear conscious are conscious
>p-zombies are possible and not prohibited by some fundamental nature of complex biological systems
>consciousness itself does not incur any benefits to survival and reproduction of a species

Even with these assumptions in place, it could be answered by the simple fact that evolution is often poorly optimized.
The common ancestor of all conscious beings developed it, even if it was some form of energy sink it just may have been so irrelevant of one that no species downstream was incentivized to lose it.