Why are the Miller-Urey experiments essential to the theory of evolution?

The Miller-Urey experiments are not necessarily essential to the theory of evolution. In fact, their findings have been questioned by many chemists and evolutionary biologists.
In short, scientists Stanley Miller and Harold Urey sought to create the chemical conditions that were present on Earth before life emerged. They then successfully created amino acids, the building blocks of organic molecules, using an electric shock intended to replicate lightning. In other words, their experiment created one plausible theory about the origins of life on Earth. However, subsequent scientists have argued that the conditions on Earth at the time of the emergence of life were different than what Miller and Urey thought.
To say that the theory of evolution depends on the conclusions of this experiment is inaccurate. For one thing, evolutionary theory and theories about the emergence of life come from related, but not identical, fields. For another, there are plenty of other theories about the origins of life, including some that emphasize the role played by comets and meteorites. Miller and Urey made the first great advance in theorizing about the emergence of life, but their conclusions are far from definitive.
https://www.scientificamerican.com/article/primordial-soup-urey-miller-evolution-experiment-repeated/