Here's why:
* Participles can end in -ed (past participles) or -ing (present participles). Examples: "baked" (past), "baking" (present).
* Gerunds always end in -ing. They are verb forms used as nouns. Example: "Swimming" is a great way to exercise.
So, while both participles and gerunds can end in -ing, only participles can end in -ed.