Why is it not possible to just consume only pure atp and thus eliminate some steps in
metabolism?

Our digestive has the steps of digestion and absorption associated with it. So all the compounds taken in as food are first broken down into simpler components before absorption.

ATP or Adenosine Triphosphate is a compound containing a molecule of adenine as nitrogen base, a ribose sugar and three molecules of phosphate attached with the adenine in a chain. Its unable to get absorbed into the system as ATP itself. In intestine, it will be broken down into Adenine, ribose, and phosphates and then absorbed individually into blood.

Thus even if we consume raw ATP, we can't bypass the process of ATP formation. So, there's no significance. And secondly, ATP is very expensive and not suitable for consumption itself.