Brittany sits next to 4 phonetic neighbors — Britney, Brittney, and Britt are the closest matches by sound. Most share Brittany's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"from Brittany, land of the Britons"
"son of the gray-haired one"
"noble desire"
"modern invented name, strength implied"
"modern American compound name"
"unit of luminous flux (scientific)"
"light, movement"
"enclosed woodland"
"Shade or darkness cast by an object blocking light"
"crowned with laurel, laurel bearer"
"dear, beloved"
"Comfort and consolation in times of distress"
"rocky land, land of rock"
"royal staff"
"God is beautiful"
"from Airelle (place in Normandy, France)"
"from Renton, town name"
"immortal"
"remembered by the Lord"
"Beorhtsige's town"
"one who bakes bread"
Similar sound: These names share phonetic patterns with Brittany — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Latin origins, giving them the same cultural heritage as Brittany.
Rhythm: Brittany is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.