Why is that country musicians who grew up singing in church are often good at singibg low notes? What factors would make them sing low notes easily? Does upbringing derermine what vocal range you will end up with or are you just born with a certain range that no southern church can do anything about? I never hear tenors in country music (more in opera and classical church choirs).
A singer's range is determined initially by genetics and then by training. There are plenty of tenors who sing country music. You are hearing nothing more than the popularity of lower voices in country music, which causes singers with lower ranges to be able to be more popular than they would in other genres, which often favor higher ranges.
Singing country or church music does not make one's range lower or higher.
The typical country vocal sound is "intimate", the sound of a close-by utterance. A rumbling voice in its comfort range is one that can retain that impression reasonable well even through a PA while screams and shouts are more of a projecting or traveling sound rather than one that is already close by.
Basically it works pretty well for the kind of sound composition typical for the genre. Country also tends to be more text-heavy than pop or rock, and the text conveys better when close-captioned at comfort pitch and volume than yelled at high pitch.
Good musicians tend to gravitate into genres where their qualities come out best, and country is a genre where a low voice happens to be an asset in the typical genre pieces and instrumental setup.