I agree that intelligence would benefit most species. But animals don't decide how they evolve, the environment does. Evolution works in tiny baby steps. So if a fish starts evolving high intelligence, but loses maneuverability because it has to sustain a higher blood flow to the brain, then predators will have an easier time killing the smarter fish. They will lose the smart-trait, and the dumb, yet more agile, fish will survive. Having a higher intelligence in this case would in fact inhibit the species.
The flaw in your argument is that you assume evolution has an end-goal. It does not.