If we think about most of the stories people present to us we would notice that there are more sad ones than happy ones by a large margin.
Why is that?
Perhaps it is because sadness is more universal than happiness. Happiness is often thought to be a momentary spark in our normally unhappy lives and almost a form of gloating when we declare that we are happy. Or perhaps we don't want to jinx ourselves by stating we are happy only to have that reversed almost immediately after our statement.
To take a different perspective perhaps working towards happiness as a constant in our lives takes too much effort to establish the habit where as sadness is a surrender to forces beyond our control which is both more acceptable and easier.