Jungle main here. Jungle can be an extremely stressful role, especially if you;re new to the role or autofilled. Plus, a good 85% of my games, I get flamed/blamed for people dying, especially to ganks. I've had plenty of laners threatening to premade 9x report me because I didn't gank enough.
That being said, when you're a jungler and all three lanes lose it's extremely demoralising, because at that point there is very little you can do. Often the weight of the game will feel like it's on your shoulders, and such stress can lead to flame.
Its dependant on the player, of course. But a lot of players can't handle that kind of stress and retaliate. It's in human nature. I myself have ragequit games just to prevent myself from hard flaming my laners.
You need a great deal of patience and endurance to play jungle. Some people don't have it, simply.