I agree to an extent. There should be a reasonable time period from which availability of software and hardware ends and the work becomes available.
It should also only apply to that particular work, and not to any of its contents (so Mario or even his depiction in Super Mario Odyssey shouldn’t become public domain just because they stopped selling the game for a few years).
I don’t think I want it to be legal for people to sell ROMs, either. I think making them public domain would do that. I know there are already people doing that, but I think the complete removal of legal repercussions would increase that.
Overall, I agree with your sentiment, but I don’t know enough about copyright law and public domain to know if I agree on the specifics.