Because you're doing different things to an image, exporting it, then returning (undo) to the original. I'm not doing this, but it's one obvious possibility.
Many things do not record in Action there may be a list of what records and what does not record. Some things that do not record in actions can be inserted if there is a menu item for it like Undo can be inserted. Stops, conditional steps and Paths can also be inserted into actions using the action palette's fly-out menu.
Crafting Actions Package UPDATED Aug 10, 2014 Added Conditional Action steps to Action Palette Tips. Contains