ELI5:Americans and Indian's going by their middle names, abbreviating first names?

How common is it for American's and Indian's to go by their middle names? I also see their first names abbreviated? Why do they still keep their first names in an abbreviated form there? Do normal people do this or is it only for famous people?

Example:

• J. Edgar Hoover,
• M. Night Shyamalan,
• P. V. Narasimha Rao,
• F. Scott Fitzgerald