I wonder if there is a kind of religiosity about such memorials, as if they were a kind of shrine? I remember being surprised in the mid seventies,when I visited a friend at Freiburg im Breisgau, how many religious shrines there were in the nearby vine-growing areas. Similarly, in a non-tourist area ofThailand in the nineties, there were many pulicly visible but obviously personal Buddhist shrines. (I presume they were Buddhist anyhow).
Perhaps some people, especially if affected by a life-shattering event, feel the need for this kind of display. Some clearly don't but it's hardly asking much of our tolerance to just accept such memorials whether we like them or not.