Point 1:
The use of "often" in the thread title does suggest a frequency over and above what is considered "normal" or "appropriate" for something that is extremely situation specific, so the general tone of judgement is somewhat offensive.
Point 2:
Even those who aren't apparently doing it for "genuine reasons" are obviously either suffering from lack of self awareness or some other issue that leads them to that behaviour. In general people can be self absorbed and thoughtless about anything. It's part of the curse of modern life - everything is performative one way and another, everything presented through the camera lens on a phone, which feeds FOMO and feeling obliged to be seen to be "nice" or doing good things. It's irritating but there we are.
Grieving people generally don't have the time or bandwidth to get too het up about it, unless it's something particularly egregious, which I have experienced, but when you're drowning in pain often you end up making like Elsa, just to avoid any more demands on your time and energy. It soon passes, the regular posting from the outer circle. Then you get the odd ones on special days, or because someone came across something that resonates, which is nice, depending.
It all really depends on the people involved, and I don't see the point of compounding or prolonging bad feelings around this sort of thing. I've been utterly furious with certain people about their outpouring of grief for my DP on social media, because in that moment it was all about me, and him, and everyone else should just fuck off. Did I do anything about it? No, bar the grumbling to closer friends in person, because anything else would just make things worse.
You know, I got to a point, before the isolation really kicked in, and I was going out and trying to socialise and it was just getting progressively more awkward, when I was considering getting a T shirt printed that said:
"Whatever you're about to say, I know you mean well, but please don't" because I wanted to save both parties from the awkwardness. Obviously it would land wrong, because we're so rubbish at dealing with death in general.
But hopefully some here will understand.