Frequency is too high. Needs to be solid metal, and your microwave uses a mesh. Your microwave is also super leaky electromagnetically, which you can see by t

Frequency is too high. Needs to be solid metal, and your microwave uses a mesh. Your microwave is also super leaky electromagnetically, which you can see by the effect on 2.4GHz WiFi. It's just not leaky enough to cook you.