This trope is more often than not Truth in Television. Abnormally large people, especially those who became larger than average at a young age, have spent their entire lives with the knowledge that they could seriously damage or even kill those around them if they don't control their strength. Whereas a smaller person's loss of control might just leave someone with some bruises, a man the size of a refrigerator is likely to cripple someone in his rage. Most of the time, they've been taught by their parents to use their strength responsibly, and often they've had a few bad experiences where they seriously hurt those around them by accident, and become incredibly tender and gentle to ensure that it doesn't happen again. Obviously not all big people are like this, as bullies and sociopaths exist in all sizes, but someone seven feet tall and as wide as a door is a whole lot more likely to be gentle than mean.