I have always assumed that it is because in its raw state it is so much better for you and contains much more fibre and nutrients (a lot of which is lost in the canning process). I guess their thinking is that you can have it as free if it is doing you good, but canned is emptier calories.
I don't know if someone once told me this or I have completely made it up, though! LOL. Sounds good though, eh?
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