zaine-h: Because Coca Cola did it first? I'm sure they were able to look at the public financial records and advertising campaigns to find what went right, what went wrong, and how to sell the hell out off it.
cjrgreen: Coca-Cola used 10-ounce cans only in Canada, where 10 Imp. oz. (284 ml, changed to 280 ml post-metrification) has long been a standard size. Master bottler Earl Dean's 6-1/2 ounce contour bottle is (was, the refillable bottles were last made in 2012) their longstanding symbol for nearly 100 years.
Reduce product size, and promote the hell out of it so consumers won't notice they're getting less for their money. Pepsico's not the only party guilty of this. Mass-market "premium" ice-cream makers have managed to get 64-ounce cartons down to 56 and now 48 ounces without any major protests.
When I get less for my money. I notice, right away and I can see that spending more money = bad. Then I stop buying those overpriced products. And I'm not a genius. So why are so many people allowing themselves to get ripped off? I'm not talking about the people who need smaller products for their lunch boxes or like the appearance of smaller products. I can understand why they don't mind. I'm talking about the people who just don't give a shit... Why? Do they have trees in their backyard that grow money for them? Are they followers of a religion that promotes being poor or throwing away money whenever possible?