Why is the smartListId not in the person object?

Hi there! I am trying to update our database when a lead moves to a new smart list. Although it's possible to get all leads in a specific smart list, it doesn't appear that it is possible to get the smart list the lead is in. Is this an oversight? The person object (at the /people/:id endpoint) does not return smartListId, even when you request allFields. It provides stageId, but not smartListId?