This is a good question. There are many social issues and some of these social issues have been around for a very long time. For example, the social problem of poverty and inequality have been around as long as human civilization. Similarly, the social problem of war also has been around for a very long time.
There are several reasons for this. First, the lessons that one generation learns are the very lessons that another generation forgets. For this reason, there are many cycles in history.
Second, there are no perfect solutions to social problems. So, what works in one context may not work in another context. Moreover, what works now may not work later.
Finally, there is something in the human heart that is selfish, which creates havoc in society.