It's such a tragedy that they're also extremely solitary animals and die shortly after reproducing the first (and only) time.

Almost all other particularly intelligent animals seem to be gregarious, and it's easy to conclude that a social lifestyle tends to select for more intelligence, a sophisticated theory of mind, and so on (I like to think that that's exactly what was responsible for a runaway intelligence explosion in humans). But in the case of cephalopods, there's something else that has been applying selection pressure towards exceptional intelligence.