Here's why:
* Blue whales are the largest animals to have ever lived on Earth. They can grow up to 100 feet long and weigh over 200 tons.
* T-Rexes were large predators, but they were still much smaller than blue whales. The largest T-Rex fossils found are estimated to be around 40 feet long and weigh around 8 tons.
So, even though T-Rex was a fearsome predator, it wouldn't even come close to the size of a blue whale!