I have a theory.
A blue whale can grow up to 30 meters long and is quite gigantic, while Titan might seem attractive to the whales, and it may have wanted to mate. A blue whale's penis can become gigantic, and with it, he has fucked up the glass. Either water leaked in, and they drowned, or the whale's penis got stuck and sealed the hole. Due to the pressure and pressure difference, the penis gets sucked in, sealing the hole. However, at the same time, the pressure difference sucks out all the whale sperm (up to 1500 liters of sperm), and they drown in the sperm. I'm not sure how the pressure works with whale penises, it was just a thought. But let's say the sperm doesn't ejaculate, and the whale's penis seals the hole and gets stuck due to the pressure. The whale panics and swims away, making it impossible to find the boat. Then they run out of oxygen.
