The demo was designed to be complete for what it is, that's why it's so polished. The game now and the demo are entirely different cause nothing in the demo was made for the long term.
You are paying for a game in active development, not a game that's complete and simply getting updates.
For example, the "no audio" issue stems from playing older versions, it seems some residual registry data from the old way the game would save (be it the demo or older versions of the current game not sure). I will release a guide on fixing this shortly. But it's just the consequences of working with dev versions.
As for the other bugs many of them should be addressed in the update today but it depends on platform. Some issues are on the back burner cause they don't exactly break the game. This project is largely a one person job, and I just hire people for certain aspects. I can't focus on every little problem mid development cause fixing one thing can break another. I focus on broader development until a time comes when polish is due. And at that time you can expect similar polish to the demo if not better.