What is "Consciousness"?
Whenever dealing with "consciousness", you'll run into the problem that too many people don't want to define it.
In fact, consciousness is simply a word we use to describe things that pass certain tests. Specifically, the ability to react to the present based on past experience. There's no terribly precise definition, as there's a large grey area that could reasonable qualify, but it's not a particularly hard problem either.
But many people want there to be some magic. Some quality that transcends the "physical" world (whatever, precisely, that means). So they claim, with no particular evidence, that there's some undefined, hard problem to solve. That we don't understand consciousness in some intractable way.
I don't claim to know every subjective opinion on the subject, but I'd wager it mostly has to do with feelings that the self is different from everything else. Feelings that make it hard to shake the notion that "I" am different from "that".
But because there's no definable trait that equates to "consciousness", there's nothing to actually prove. The burden is on those who claim there's some yet-undefined "consciousness" to prove that it actually exists before we can question how or why it exists.
Consciousness is a Product of Learning Algorithms
As long as we define consciousness in a meaningful, testable way, it's not that hard to explain how it exists. Since consciousness, by any normal definition, is just the ability to learn from the past to make present decisions that (hopefully) lead to a better future outcome (that is, the state of having a rational mind), it must involve learning. Learning requires some type of base programming with "good" and "bad" reinforcements, and an environment that triggers these reinforcements.
While abiogenesis isn't a 100% solved issue (we can't exactly portal back in time to prove anything), it's not difficult to come up with educated guesses about how it happened. From there, it's trivial (with modern scientific understanding to lean on) to show how biological evolution works, which eventually led to neural networks, which led to consciousness.
Consciousness is not Fundamental, and is therefore not a Brute Fact
A "brute fact", as I understand it, is a fact that is so low-level we can't offer any explanation for it beyond "because that's how reality works". The Big Bang happened. We can make some wacky guesses for things that caused it (a cosmic, 684-dimensional kid skipping a cosmic rock across a cosmic pond and we're the ripple that ensued), but there's no actual evidence to support any such thing. So the Big Bang, for now at least, is brute fact.
Massive objects (relativistic energy, whatever you want to call it) cause other massive objects to move towards each other. We have math that predicts the motion of objects due to gravity, either in the less accurate approximation of Newtonian mechanics, or the more accurate Einsteinean relativistic mechanics. But we don't have any way to explain why massive objects create forces (or bend spacetime) the way they do. So gravity is a brute fact.
Anything arising from brute facts is "explainable" as a product of those brute facts, and is not itself a brute fact.
Because consciousness is easily-enough explained as a product of learning, which is a product of neural nets, which is a product of biological evolution, which is a product of chemistry, which is a product of quantum mechanics, it is far removed from being a brute fact.