Why is a pressure cooker unsuitable for achieving a crisp, seared exterior via the Maillard reaction?

It requires direct, dry, high heat.

The Maillard reaction, responsible for creating deep, savory flavors and desirable browning or crispness on surfaces like meat or vegetables, is a chemical process highly dependent on specific environmental conditions. This reaction necessitates the presence of direct, dry heat, which allows surface moisture to evaporate, concentrating heat energy and facilitating the complex interaction between amino acids and reducing sugars. A pressure cooker fundamentally operates in a sealed, wet, high-pressure environment. This constant presence of moisture inhibits the necessary dehydration and high-temperature concentration required for browning and searing, meaning that while it excels at tenderizing tough internal structures, it cannot deliver the surface texture critical to roasted or sautéed dishes.