Because it's not about food, but the challenge? Without the roadrunner, Wile E. is nothing. He depends on not succeeding. (Just noticed what a great role model he is.)
According to certain versions, Chuck Jones and his team established a set of rules for the cartoon (such as "The audience's sympathy must remain with the Coyote" and "Whenever possible, make gravity the Coyote's greatest enemy"). One of them is supposed to have been:
The Coyote could stop anytime—IF he were not a fanatic. (Repeat: "A fanatic is one who redoubles his effort when he has forgotten his aim." —George Santayana).
Here's the new thread for posting quotes, with the usual rules: