OP, I think that the very articulate comment from furfoxsake explains why your comment that "its to make the parents feel good, it doesn't help the child" is inaccurate.
In the case of my friend who just lost her child, putting photos of him on fb helped to create a huge outpouring of support for both her AND her DS. Furthermore, it helped to educate people about children and cancer and the resources available to help them. Lots of us made and are making donations to an organisation that brought joy to her DS during (what we didn't know would be) his final months.
It's also a false opposition to distinguish helping the parents from "helping the child". The demands on the parents of a severely ill child are enormous, and helping the parents IS helping the child.
Parents love their DC, and like it or not, DC who are gravely ill remain their DC. People post photos of their DC on fb all the time. Why should parents NOT post photos of their ill children just because it offends sensibilities like yours? Should the parents wait until the children are "well enough" not to make you feel squeamish?
My friend's DS was ill, but he was still his beautiful self. He didn't need to be hidden away from a larger community of family and friends.
I am willing to believe that you mean well, OP, but you still don't get it. Your tears of loss are not falling on the computer keys as you type. Please don't dictate to other parents when it comes to coping with suffering.