Why Do So Many Cephalopods Die Immediately After Reproducing?

Why do so many cephalopods die immediately after reproducing?

Okay so the physical reason is that mating triggers a change in their brain chemistry and hormone levels that essentially poisons them and makes them behave strangely and stop eating. If the gland responsible for this change is removed, the cephalopod continues as normal and lives for many months after laying eggs.

But the evolutionary reason is the end-Cretaceous extinction. Cephalopods used to have a pretty huge variation in lifespan, ranging from a few months to over 200 years (https://www.iflscience.com/ancient-paperclipshaped-sea-creature-could-live-for-200-years-57685)

IFLScience

Ancient Paperclip-Shaped Sea Creature Could Live For 200 Years

Ancient Paperclip-Shaped Sea Creature Could Live For 200 Years

Large, long-lived cephalopods were hit hard by the mass extinction and those who survived did so by being short-lived and reproducing quickly, so they were selected for as cephalopods recovered from the extinction event. The most ancient species, the nautilus, can live for several decades and mate many times, hinting at the high diversity of life strategies that cephalopods used to have.

So yeah, the reason octopuses usually only live a year or two before self-destructing is because of that fucking asteroid.