Because it wasn't cooked correctly.I have tried it three times, I'm out on octopus. I find the texture horrible.
In order for octopus to be cooked and taste great, you first cook in pressure cooker for 30 min in water, with some oil, salt, peppercorn. The octopus will be like butter texture. Then you can add sauce, marinates like sunflower oil or dry rub with paprika and garlic, or mix with salad. I learned how to cook octopus while living in the islands.