Stack ability is the result of the base of a three piece can (3pc) fitting in the top. Most 3pc food cans have the same diameter top and base and do not stack, the merchandising does not require stacking. This is however slowly changing, making the change requires a tooling investment but will mean less material so savings overtime can be réalisés. In Europe stackable cans are widely used, the other type of food can is two piece and these have the stacking feature. The stacking in 3pc(2pc?) was driven mainly by the retailers. In the US most food cans are two piece so they stack, the 3pc cans do not stack as the top and bottom are the same diameter.
The rest of the world by and large follows the US on 3pc can & end design, so the 3pc cans do not stack, but it may be that overtime this changes