diminishing returns
1. In economics, a yield rate (i.e., of profits, production, benefits, etc.) that fails to grow in proportion to the amount of investment, skill, time, or effort that is added. The restaurant, to combat high volumes of customers, hired a large surplus of wait staff and cooks. This led to diminishing returns, however, as the overcrowded staff was far less efficient and eventually cost the restaurant more in wages than it was earning.
2. By extension, any output or results (e.g., of a product, project, organization, etc.) that fail to increase proportionally to additional time, money, skill, or effort. Unfortunately, the show's charm has not lasted, and the infusion of zanier plots has created diminishing returns in terms of quality.