that the moment a physical book is published and sold through it immediately becomes “not available for sale”

Because that specific book now has a new owner who can keep it or sell it as they see fit. Like people still do with physical games.

If you mean that a book becomes generally unavailable when it’s between printings, though, you’re wrong.

Publishers overlap print runs and begin selling the first paperbacks before they’ve sold out the initial hard cover prints PRECISELY to avoid the situation you seem to think happens with every single book.

It’s heavily affected by the fact that I used to listen to After the Revolution to fall asleep (in a good way! It’s a great book and Robert Evans’ voice is soothing IMO), but here’s mine: