The main disadvantage octopi have is their antisocial behavior. The parents don’t raise and teach their young. They live in solitude. The only time they spent time together is for mating, after which they die.

Octopuses that can talk to each other, hunt in groups, and raise their young collectively would be pretty formidable. Even if they managed to get there, they would still be living underwater making the use of fire pretty difficult.

Children of Ruin is a great book that describes a civilization of octopus, if you want to explore this a bit.