It's just survival - when a species gets good enough at survival, it learns to adapt to the environment. First, it's just simple reflex, trigger and response, but with evolution, species have become more capable to adapt. We, humans, need to adapt not just to nature, but also to the human society and technology, and human consciousness is just that function. Without it we would be dead of hunger and thirst in 3 days. What is special about conscious systems is that they adapt and preserve themselves in the face of adversity.

Pleasure and pain are related to reward signalling in reinforcement learning. Humans have inborn reward signals which have been selected by evolution. Artificial agents have reward signals too, but they are designed.

So I think the path to consciousness is to create artificial agents that learn to survive and adapt. When such a complex behavioral system is designed, it naturally learns about its relation to the world. It has consciousness by extension of being capable to protect its life.