|SUM(score) as total_score,|
|SUM(a.c) as mention_count,|
|ROUND(SUM(score) / SUM(a.c), 2) as avg_score|
|SUM(a.score) AS score,|
|COUNT(1) AS c|
|SPLIT(REGEXP_REPLACE(title, '[^a-zA-Z ]', ''), ' ') AS word,|
|a.word = b.aka|
|GROUP BY b.country|
|HAVING mention_count >= 100|
|ORDER BY avg_score DESC|
Your query doesn't pick up any countries with multi-word names (e.g. South Africa, North/South Korea) except for the ones that have single word aliases (e.g. USA, UAE, Saudi).
According to your results South Africa and the Koreas have never been mentioned on HN or Reddit which is obviously not true.