All of the cookie cutters on the site are 3D Printed, instead of produced through injection molding. This makes it possible for me to have an extremely wide variety of designs to choose from, since it doesn't matter that much if a design is only ever ordered a handfull of times.
Injection molding requires a significant upfront investment, as the aluminum molds can cost $500+ each to make. A $500 mold for a $6 cookie cutter that only ever gets ordered 5 times is obviously a waste.
3D Printing offers the better option here since every single cutter costs the same to produce. About 1-3 hours of printing, and less than a dollar of plastic.
3D Printing is a process where layers of plastic are laid down, one at a time, progressively up, until the whole object is complete.
Here's a good video that explains the process.