Not that I really want to tick people off, but I suspect that a certain percent of motivation for doing this is to make oneself feel "special" through demonstrating that they are suffering.
In my high school we had a rather high mortality rate among boys, mainly due to farm accidents, and immediately after a death, a certain percentage of the girls would all of a sudden develop romantic ties to the dead guy, or enlarge the romantic tie that was there. They would sometimes even have conflict over who was suffering the most. As if suffering was a zero-sum game.
Everyone wants to be noticed, and to feel special. This public expression is another way of doing that, I think. Frankly, I feel the temptation from time to time myself.
Of course, my new superpower of cynicism may just be shining through instead.... Okay, I admit. I am Cynical-Man(tm)