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)"
"nobleman, pledge"
"The great; the large"
"raven"
"old, wise ruler"
"skilled metalworker"
"the strait, narrow waterway"
"alder tree dweller"
"glory of the homeland"
"sunray, shining light"
"Ford by the windy place; a river crossing in a breezy location"
"field settlement"
"daylight, the day"
"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.