The original purpose of collars was for cooler weather. To tie a necktie around it to insulate your body from the cold air. That combined with a suit jacket kept you warm.
This became the standard of mens wear in northern cities like London and Manhattan.
But at some point the southern U.S. and southwest U.S. developed. Latin America, Africa, middle-east, etc. are developing. It's just odd to expect something northern-specific to be the standard everywhere.
But nowadays, collars are a vestige. People wear it just because it associated with formality, rather than any actual purpose.