The United States is known for having its Founding Fathers, not its Co-founding Fathers. The term Founder doesn't imply exclusivity, rather the use of "The" vs. "A" makes that distinction - someone is A Founder of a company or THE Founder of a company.
So I'm curious, how did that industry get to the point of using Co- and why?
I suppose the question could also be asked this way, is it wrong to refer to a group of founding individuals of a startup as each being "Founder"?