'Cause goats don't eat grass.
Goats will eat everything else but grass. In my personal experience, goats will eat pine tree seedlings by the hundreds, lettuce, cucumbers, tomatoes, blackberry leaves (but not stems), roses, corn, and pigweed (as a next to the last resort).
After all those are gone the bastards will eat grass.
My goat, Sheba, was a delightful buddy, much like a dog, but she would eat grass only after she had destroyed everything else.