Evolution doesn’t make deliberate, strategic choices. Random mutations result in new behaviors/properties that may or may not be beneficial, and selection removes those mutations that prevent reproduction from the gene pool. Not every mutation will be beneficial, but as long as it’s not harmful enough to stop reproduction, it can persist.

If there were two groups of octopuses, one with the self-destructive behavior and one without, then there would be pressure from competition. In that situation, your point would have more of an impact. But without that pressure, there’s nothing to drive the selection. And the mutation won’t occur just because it would be helpful for it to do so - it’s random.

At least, that’s how I understand it. I’m not a biologist or anything.