because we are a sad nation sheep-herded into the supermarket to by the foreign imports they wish to peddle on us. Ok a more realistic and less controversial answer - because like all foodstuffs it's down to supply and demand and whereas gala, golden delicious, braeburn are grown in bucketloads and cheap to produce, russetts, pippins, etc are not and as such are more expensive to buy so the average consumer thinks "i'm not buying those apples @ 80p/lb when these are 40p/lb" and the russetts don't sell. This is symptomatic of the blindfolded "sheep-herding" control of our consumerism by the supermarkets; we eat what they want us to eat - the solution? stop buying supermarket produce and get into the market place or high street fruit and veg, where you are more likely to see a russett etc. if they don't sell them ask why not and more often than not they will take notice and try to get them for you next time (whereas a supermarket will certainly not!)