Here is why...
Look at the image below! I did no altering of any of the images here. I simply scanned them and put them side by side for comparison. Notice that the professional lab prints the closest to my edit, whereas the other "quick print" places alter the coloring and the images look a bit washed out. The printers at these places just can't do justice to the images produced by a professional camera.
You spend money to hire a professional photographer, you should be getting professional prints as well! That is why ALL of my packages include a gallery store credit. I want you to be able to display beautiful artwork from your session in your home.