A bit similar process in sea-dwelling salmons: migrating from salt water into fresh water (quite a big metabolic challenge in itself), traveling up rapids to suitable spawning places (often a long and arduous journey)... after they've accomplished that, their chances of returning alive are quite low. So they mostly die. But their close relatives, river-dwelling trouts spawn many times in life, because their migration isn't as costly.

I would suspect that something in how octopuses reproduce has an element of "return being costly" - it could be a metabolic return to the feeding and growing state instead of a physical return.