Why was coors beer illegal east of Texas in the 70s?

Coors chose not to obtain licenses to distribute in states east of the Mississippi due to concerns about competition with other major brewing companies and quality after transportation. Coors had only limited production facilities and insisted on refrigerated shipping and handling. They were trying to insure a quality product. Additionally, there was an agreement between Coors and Miller - Miller would be east of the Mississippi and Coors the west of it. Until the early 80's when both went national.