The death of public figures (and this did seem to begin with Princes Diana) has a peculiar cultural impact in uniting people in what is really pseduo-grief. They are not actually mourning someone they did not know, they are bonding together to share a common experience, because this gives people some feeling of comfort and belonging. This continues with visitng specified location and leaving a 'tribute' -however inappropriate that might be.
A similar knee-jerk reaction is to focus in on the nearest (in time) tragedy, and offer spurious comparions. Again, this allows poeple to feel righteous about their own particualr 'grieving' focus - and again it is something deeper than the apparent issue being discussed.
A better example of this mass bonding behaviour - and it occurs on here at regular intervals - is the need to out-do others with a level of outrage at the latest attrocity. This usually takes the form of wishing an accused individual a seriously nasty death, with the poster usually on hand to offer to administer it if no-one else feels up to the job.
So the wailing and ghnashing of teeth, and the obverse sneering and laughing are really manifestations of the same trait in human behaviour - a feeling of a need to 'belong' and bond together with a common cause.
It passes off after a short time, or is replaced by something else, because lack of direct involvement means that such feelings are as brief as they are intense, so wait a few days, and everything will settle down.