But why the need to replace shared public playgrounds with your own versions?

As has already been mentioned by others in this discussion what do you do when your children outgrow these toys? They get thrown out, along with your neighbors, and their neighbors, etc...

We no longer share public spaces with others, instead selfishly insisting on our own private versions. When they outlast their limited life span, it's just more garbage to be added to the landfills.