Why? Because we haven't got our emotions by chance. All above mentioned emotions have a common theme and that is that they are usually suppressed by us. If we do that for a long time (and we have learned that) you can eventually get physical and emotional complaints, because the energy no longer flows properly through your body. All our emotions just want to be recognized and felt, because they are necessary for our growth and well-being.
So every time something serious happens, we have the opportunity to feel and express the accompanying emotions. It is not necessary to express them to the person(s) concerned and it is not about the situation either. They are just triggers to help you allow these emotions to be, without suppressing, just as you allow your nice emotions to be. That way you return to your authentic state of inner peace and harmony, because you don't have to fight, suppress or ignore them anymore. You acknowledge both the light and the dark part of yourself. This is how you can really love yourself unconditionally. What a beautiful reason!