Some writers start by asking “what applies to every person in the world?”
What a dull question.
Subjects with mass appeal get more attention. Cool. Fine. Mad respect for anyone who can target mass audiences consistently and do it well. How you do it without jumping out a window is a mystery.
Generally speaking, nonfiction writing itself is not a profession. It is a means of expression. What do you wish would be expressed more? Write that.
“People love what other people are passionate about.”
— Damien Chazelle