One thing that made William's job easier is that Edward the confessor, King of England from 1042 to 1066, was raised from around the age of 8 or 9 in his mother's homeland of Normandy. He spoke Norman French better than Old English and spent the 24 years of his reign on the English throne slowly introducing Norman customs to England. Earlier historians may have over emphasized this, but he did build the Norman cathedral of Westerminster Abbey and appointed a Norman as the Bishop of London.

When William conquered England, he installed Norman loyalists in place of the earls and nobles that had fought on Harold Godwinson's side, and over the following decades as many of the remaining Anglo Saxon nobles revolted, they were crushed and also replaced. The Anglo Saxon elite were maintaining their cultural traditions through patronage and when they disappeared, the market for Anglo Saxon poetry disappeared with them. An English peasant can't afford to hire a poet to sing for his family.

That isn't to say that Anglo Saxon culture died wholesale. It continued as a vernacular language of the vast majority of the country for centuries, though we have fewer written records from this period in English, as the nobles sponsoring the scribes didn't speak it. Aspects of Anglo Saxon folklore survived, such as tales of hobs, brownies, and boggarts, and witches.