The most successful attacks are the ones that go unnoticed and do not alert the system as a whole, or convince the system that they do not exist. Invisible parasites, subtle entrances, etc.

An exploit that straightforwardly pillages an ecosystem (as long as it's not utterly destroyed) will immediately produce anti-bodies/defenses against the attack. It will alert other systems that are vulnerable to the attack.

An exploit that slips between the cracks unnoticed and siphons energy or resources or mindshare is infinitely more effective.