Because we define "instinct" in a way that separates the behavior of animals from humans and we have evidence from both personal experience and observing the behavior of other higher primates that humans are capable of operating beyond their instincts, for instance by creating social and political abstractions which optimize for things other than survival and procreation. The existence of art, language, science, philosophy and law cannot be reduced to purely instinctual drives.
This is a profoundly uninteresting and juvenile line of argument which inevitably reduces to solipsism.
>Bears are smart. They can't design bearproof trash cans for national parks because the smartest bears are smarter than the dumbest national park visitors.
Humans split the atom, sequenced genomes and went to the moon. We can't design bearproof trash cans because those trash cans have to be usable by humans, which creates fundamental engineering weaknesses that animals can exploit, not because bears are smarter than humans.