Google not showing the parent article on SERP, it shows the child article.

Google not showing the parent article on SERP, it shows the child article.

Example:

I have created an article “What is GST”. Under this article, there are many child pages like “How to generate EWAY bill without GST number?”, " How can I cancel e way bill after 24 hours?", “What is GST tax?”, “What is Part B in e way Bill?” etc.

When I search the term “What is GST”, the main page does not appear in almost till 10th page of google while child page like “What is Part B in e way Bill” appear in the first page. what is the issue?

It’s tough to rank for short / generic keywords. So I think that is a reason. However, when you write on long tail keywords it might rank.