The subjective feeling is just a brain state. The ‘why’ is due to whatever circumstances resulted in that brain state.

But one can definitely ask how something seemingly as complex as a "brain state" can be directly experienced as phenomenology. How is it that we can so easily describe some things about our brain states, that we'd never realize by physically looking at what brains do and how they behave.

That's the "hard problem" of conciousness stated simply, and the answer to it would seemingly have to involve some quite direct access to some part of brain state physics - meaning that the physical properties involved are quite "basic" in some sense.

> How is it that we can so easily describe some things about our brain states, that we'd never realize by physically looking at what brains do and how they behave.

As a software developer, this should be simple. Programs have their own state that you can understand without knowing the exact formulations of electrons in the processor that ultimately make up that state.

X = 5 sure but good luck figuring that out looking at the motherboard of a running computer.

So why are some brain states conscious and not others?

It would be impossible for the organism to operate effectively if they were conscious of every single thing going on in their brain at all times. In fact many things you aren't normally conscious of, if you focus, you can become conscious of for the moment.

There is no reason to expect that the self-aware conscious mind has full access to everything that is going on in the brain. In fact, from both an evolutionary and systems perspective, that would be extremely surprising.

Good luck getting to the roots of all your feelings when they can be based on any number of inputs and changes over who knows how long of a time.