When you get a Full Gallery of Images, it's not every single image captured in the camera; it's every single GOOD image captured in the camera. Sometimes I attempt to capture a fleeting moment... and fail. The subject turns away, or there's just not enough time to react. I call this 'taking risks', going for hard shots that might not work. Sometimes I need several attempts to nail the image I'm looking for, and those failed attempts look like a disaster! I don't process those images. Noone wants to see the blurry back of a person's head, and you certainly don't want to be paying for the privilege.
Sometimes I take 'safety shots'. A good example of a safety shot is the five other photos I take for a posed group moment to make sure I get at least one where everyone has their eyes open! This works great for everyone because you don't have to wait for me to check every single eyelid in the photo when I'm taking them. Later I'll pick the best one from the set and just process that one.
So the Full Gallery is a huge number of processed images, but still only a fraction of the images taken. A full day wedding will result in upwards of 700 processed photos... possibly over a thousand if there are many guests and lots happening.