If you go into your Steam library, click "Add a Game" on the lower left, and then go to "Add a non-steam game", you can navigate to the Aurora executable and add Aurora to your Steam library. That way, you can have Aurora on Steam without needing it to be on the storefront.
If you want it on the storefront, I don't want to speak for Steve here but every bit of my understanding of the intent and purpose of Aurora as Steve's project is that he does works on it for himself, to create interesting stories that he has an interest with. Throwing it on the Steam storefront, even if free, would put some amount of pressure or "implicit obligations" on him to change the game in ways that he has no interest or disagrees with. I imagine he'd sooner just make the game not accessible at all.