For what reason can't a dentist simply remove the second molar just before the wisdom tooth instead of removing the wisdom tooth that is impacted?

Second molars: He\she can. However, the wisdom tooth would rarely move into the same position previously occupied by the second molar, thereby creating spaces and potential caries and periodontal problems. We wish it were that simple and easy. The wisdom teeth are usually smaller and due to their root formation, less stable and strong. Timing would be crucial when this is attempted. Orthodontics might be needed.

Common Sense: It's common sense to remove a tooth that has shorter roots, is difficult to keep clean, and is prone to cavities. Why remove a healthy second molar? The impacted tooth may never erupt correctly into the space, and will not occlude correctly with the opposing dentition. It's also the standard of care.... Second molars are extracted only when hopeless.