Why have psychological motivational theories become more prevalent than scientific management in the modern business world?

What will be an ideal response?

Answer: Most of today's jobs require more intellectual capacity and less manual labor. Increasing the productivity of workers with intellectual responsibilities is better achieved by understanding them psychologically and motivating them to perform better.
Explanation: Work has evolved to become less manual and more intellectual since scientific management was introduced in the 1920s. Psychological motivation of intellectual workers is more effective at increasing productivity, whereas scientific management seeks to improve productivity of manual tasks.