Why do 2.5 or 3 gallon cornelius kegs cost more than the five gallon version?!
Answers: It is all in the production volume. Fixed costs like breaking, rolling and welding equipment is divided among the total kegs produced. The more common units have lower per keg fixed costs that don't offset the material savings. Same issues affect us in the industry with 1/6 and 1/2 bbl cooperage!
Smaller portions of just about anything are more expensive to produce. Mostly because of volume/common sizes and marketing.
They make fewer of them a std batch is 5 gallons