Why do sharks leave blue whales alone? Couldn't they just rip some parts off the slow, helpless whale?

Look at this giant:

Blue whales are not just big; they are the biggest animals on Earth and the biggest animal that ever lived. If I were a 4,000-pound shark, I wouldn't face a 400,000-pound whale 100 times my size. The only predators of the largest animal on the planet are orcas.

However, it takes a group of 50 to 75 killer whales to attack just one. Even if you were a killer whale, you would have no chance of catching a blue whale, not even if you were in a group of 30.

So if it takes up to 75 orcas to attack a blue whale, how would a single large white whale fare?

Too damn bad.

Here is the shark compared to the whale:

Blue whale at the top, humpback whale in the middle, great white shark at the bottom.

As you can see, the blue whale is absolutely gigantic when compared to a great white shark. Even compared to a humpback whale, the blue whale is huge.

One reason lone sharks don't attack these beasts is their tail. A lone slap from the whale's tail would destroy a car. Imagine what that would do to a shark.

Most seals are much easier prey, are less powerful and don't have bone-breaking tails. I would say a large elephant seal would be able to successfully defend itself against most sharks.

Blue whales are also one of the loudest animals. Being able to produce 180 decibels, these mammals can burst your eardrums. If a shark heard this noise next to the animal, it would definitely die.

So yes. Sharks leave blue whales alone because they don't stand a chance against them.

Now moving on to the second question.

It would be almost impossible for the blubber to be penetrated. Occasionally it can grow up to 1.2 meters (4 feet) thick! If the blubber could get that thick, it would be nearly immune to predator bites. On average, it will be 30 centimeters (14 inches), which is not as thick as the maximum, but still very difficult for a shark to bite. Ocean predators aren't used to piercing animals so protectively, which may be another reason why the blue whale has very few meat eaters to worry about.