The Shuttle Orbiter (the reusable part) was not a complete stage as it used an expendable external tank. It did reuse the engines, which one would imagine would

The Shuttle Orbiter (the reusable part) was not a complete stage as it used an expendable external tank. It did reuse the engines, which one would imagine would be a significant cost savings, but the Shuttle system was such a complex and compromised beast that it ended up being one of the most expensive launch vehicles of all time. Vertical landing for the Falcon 9 made sense because it meant they only had to add a small amount of extra weight and new systems (landing legs, grid fins, etc.) in order to achieve powered precision landings. In contrast, adding wings, landing gear, other aerodynamic components, and potentially other engines (in order to achieve powered landings) adds a lot of extra complexity and weight. Additionally, the stage is already designed to handle vertical flight and forces, making it strong enough to handle strong aerodynamic forces while flying horizontally is no small change. And vertical landing enables barge landings out at sea as well as dramatically reducing the size of the landing facilities (a small pad versus a landing strip). All of which saves costs, complexity, and enables a higher percentage of the vehicle's performance to be used by the customer versus for recovery.