Why do people act like my feelings emerge from a vacuum all the time?

I try very hard to manage my emotions because they cause me lots of trouble. But I just fail to understand this: People treat my emotional *reactions* to things as... harassment on them. It's like they don't get that my feelings happened for a reason even if they happened too intensely, outside of my control.

It's as if I'm not a person to them anymore but a bomb that will go off unexpectedly and without reason. None of my reasons matter. Their reasons are more important than mine.