Because Nikon haven't done it yet. Once they do, wait 3 years and hey-presto Canon will have it too (or 6 years after Sony).
I must admit, I don't use a lot of the add-on bit's and pieces that are already in DSLRs (e.g. HDR), but the really useful things seem to get left out, which is why I 'have' to have ML installed.
If they won't even do auto ISO stuff right (well until somewhat recently and then only with some models), what is the chance of a really advanced feature like auto-panoramas?
BTW, I don't know what software Apple uses, but Canon doesn't even have a good photostitch outside the camera, how are they going to put an automatic one inside?