Note: This post is not about the concept of present perfect. It's not about the general rules either. It is about real life context. I know the general rules I just don't know how do I use some of those in this particular situation. Telling the general rules again does not always help solve specific questions, right?
When describing something happened, people usually use "it's what happened" or "it's what has happened".
However, Google Ngram indicates the former is much more commonly used than the latter, why is that?
Does they mean the same? Could someone please give a hint? Thanks in advance.