Was told similar years ago. Also told reason was that most of them "checkout chicks" , not my terminology, were under the age of 18 and therefore illegal to handle smokes. The big 2 also believe that they have foot in both camps healthy v's others as they are happy to sell smokes but you don't get your so called super dooper 4cents a Litre discount, bear in mind that the so called loyalty freebee is only good for 150L or $6.00. I'm sure any genuine price comparison check including IGA and ALDI would indicate that the big 2 have well and truly covered the cost of their so called "loyalty freebee".
The head shaking joke of it all is that you hear of people buying anything to ensure that they have the required $30.00 worth, even when only going in to get a loaf of bread and a 2L milk. I know it's a little different in the big smoke but in the scrub you often need to go a few k's to get to the required discount fuel going straight past other servo's. Yep, shopper discount fuel is a real winner - not IMHO.