And in all actuality, it takes more work to clean up each photo you deliver, and thus "costs more" than if they would have just used a makeup consultant. That is usually once and done for most of the event, but if not, then each photo comes with its own complications, and to touch up each photo should rightfully cost something to the clients, and shouldn't be part of the standard fare.
I put a fee into my senior portraits package that will cost a bit more to touch up photos. Some do it, some do not. I do a very light general softening using Nik tools as my standard processing, but to remove acne from each shot, that costs extra.
Either all the trim in my house could be stained and coated in bulk in the garage before application, or they can all go on with no finish into each room with all the hardware and paint already in place, then individually stained and coated after the fact. Which takes more time, and thus more cost?