Why did a contemporary Rip Van Winkle have to get educated to read the English

If a contemporary Rip Van Winkle had slept for forty years and awakened today, he would have to go back to school before he could understand a daily newspaper or a magazine. Many new words have been added to the English language in the past forty years; and since Shakespeare’s time the number of words in the language has increased more than five times, from about 140,000 to somewhere between 700,000 and 800,000. Most of these new words have not come from borrowing, but from the natural growth of language-adaptation of elements already in the language.
     The language has always changed, but the rate of change has been uneven. The most important of these periods occurred during the two hundred and fifty years after 1066, the year the Norman conquered England. Before the conquest, the inhabitants of England spoke Anglo-Saxon, a complex Germanic language. The Normans were Norsemen who, after generations of raiding, had settled in northern France in the tenth century and by 1066 were speaking a form of French. After their conquest of England they instituted Norman French as the dominant language--the language of the upper classes, of law, of government, and of such commerce as there was.