I can give a partial answer to that. During breakfast the kitchen item selection is pretty much limited to meat, cheese, egg and bread (some exceptions, of course). Therefore as long as someone is stationed exclusively to toast bread and bake muffins, kitchen speed usually doesn’t hinder.
Switch that to dinner, and you have multiple toppings to account for on top of meat, cheese, eggs, and bread. In addition, many people are very specific about what toppings they want on their burger (One person in particular wants pickles ONLY on the left half of their burger. Trust me on this, I’ve gotten a complaint on the 1800# because there were pickles on the right half…) which can hinder the speed as well.
It’s either that, or they aren’t following the MFY procedures, and just making extra breakfast sandwiches, since there is so much less to customize.