Thankfulness works in different ways for different people. For the one who was born with very good health it may prolong their life (may be even by seven years). while who are born with a genetic diseases - as some families have married for centuries close relatives - may have (not all) - then the baby born with a brain tumor or enzyme deficiency - still the parents can thank for the experience which will make them kinder and gentler people towards others.
It is wise to refrain projecting ones own personal experiences and psychological view points into any book of wisdom. We say - in my family - "Alhamdulillah Kulla Haga" - daily. means - Thank you God no matter what.
Otherwise how can the Muslims survive this huge carnage in this century? that is how we survive - By The Grace of God's Mercy to be humble and hope for a better life in the Afterlife. Thank you for reading.