Often, what's good for species evolution is really bad for some individuals. What good is a half-full glass to you if you're dead?

Also, as was noted elsewhere in the discussions, evolutionary pressure for bacteria to attain an immunity is high, but pressure to lose one is usually much lower. However, bacteria are small, and such pressure is higher than in more complex celled creatures. "Shelving" antibiotics does work, but would require widespread cooperation and the curbing of feeding antibiotics to livestock.