What you're talking about is the authors not reporting variables they considered, and then didn't control for. These not being reported is not universal - for example, I very frequently report every variable considered, and make my code available, with comments about variable selection within.
What the parent post is talking about is "unmeasured confounding", or a Rumsfeldian "Unknown Unknown". If there is something that matters for your estimate, but you're unaware it exists, by definition you can neither report it nor control for it.
What you're talking about is the authors not reporting variables they considered, and then didn't control for. These not being reported is not universal - for example, I very frequently report every variable considered, and make my code available, with comments about variable selection within.
What the parent post is talking about is "unmeasured confounding", or a Rumsfeldian "Unknown Unknown". If there is something that matters for your estimate, but you're unaware it exists, by definition you can neither report it nor control for it.