Although the Normans spoke a dialect of French, they were not themselves of French descent. Actually they came originally from Scandinavia - principally Denmark. What's more, they hated the French and the French hated them!
The English language has never been shy about adopting words from other languages, if they filled a need. And that principle clearly applied to names, too. That's why English is probably the richest and most subtly expressive language in the world.