Doug sits next to 4 phonetic neighbors — Dug, Dug, and Bug are the closest matches by sound. Most share Doug's Scottish cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"dark river, dark stream"
"loving, affectionate (if from Philemon)"
"field settlement"
"glory of the homeland"
"elder counsel"
"olive tree; symbol of peace and wisdom"
"from the alder grove"
"little raven"
"sunray, shining light"
"skilled metalworker"
"nobleman, pledge"
"Ford by the windy place; a river crossing in a breezy location"
"daylight, the day"
"The great; the large"
"the strait, narrow waterway"
"house of God (possible Bethel derivation)"
Similar sound: These names share phonetic patterns with Doug — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Scottish Gaelic origins, giving them the same cultural heritage as Doug.
Rhythm: Doug is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.