Traditional jams require a good amount of sugar, or a very long cooking time, to thicken up to the correct consistency. (couldntbeparve.com)
In traditional jam making, it's that pectin (natural or added) mixed with a good amount of sugar over heat that sets the jam (and gives it it's longevity). (forkknifeswoon.com)
It is made with a good amount of sugar added to the flour with eggs to bind it together. (shortbreadsouth.com)