Why did the us organizational structure shift from product grouping in the 1950s to a matrix in the 1980s?

I hope this is right. I think it is. 
The United States had a large homogenous market which lent itself to nationwide brand and product division management. In 1954, P&G created individual operating divisions to better manage growing lines of products, each with its own line and staff organizations. I'm sorry if it's wrong. :(