Here's why:
* The Norman Conquest: In 1066, William the Conqueror, Duke of Normandy, defeated the English at the Battle of Hastings. This marked the beginning of Norman rule in England, and with it came the influx of Norman French speakers into positions of power.
* Language of the Elite: Norman French became the language of the court, government, law, and the aristocracy. This meant that English speakers were constantly exposed to it, especially in areas like education and legal proceedings.
* Vocabulary Expansion: English adopted a massive amount of vocabulary from Norman French, covering areas like government, law, food, religion, and even everyday objects. Words like "justice," "parliament," "beef," "church," and "castle" all have French origins.
* Grammar and Pronunciation: While not as drastic as the vocabulary change, Norman French also influenced English grammar and pronunciation. For example, the loss of many grammatical endings in English likely resulted from Norman French influence.
While other languages also contributed to English during this period, such as Old Norse and Latin, the scale and impact of Norman French were significantly greater, transforming the language into the modern English we know today.