In the 60s, nearly all beverage cans were a seamed wraparound of tin-plated steel. The story goes on.
Aluminum costs more than steel, and the price has been rising.
And there is competition from other materials as well. We h ave to find ways to make cans lighter and lighter to keep fending off polymers, steel and glass. Lighter cans means lower prices to the consumer, who's then more likely to buy cans off the grocery shelf instead of two-liter bottles or glass. In the 1970s the aluminum in beverage cans was nearly as thick as aluminum gutters, .015 inches. Lightweighting progress leveled-off in the early 80s, then resumed in 1984 due in part to computer modeling.