You would be surprised. Universities pay substantially better than newspapers (likely with better job security), and writing jobs are typically hard to find and low-paying in general. Many former experienced journalists end up working at university press departments because of the better working conditions.

From an enjoyment side, writing is hard, but for a lot of people, it's much easier than research. There are fewer credentials needed for a career in science journalism versus scientific research (a Bachelor's only versus a PhD for many senior scientist positions). I know a lot of people who have a natural skill at writing who decided to major in a science field for one reason or another, performed okay-ish at their courses, and tried to get back to writing work.

The end result is also similar writing for a magazine/newspaper versus a university. A university may have higher standards for accuracy and precision (especially if an interviewed scientist wants to review it, while a newspaper/magazine may have a policy to avoid sharing drafts to avoid bias in the article). However, higher-end magazines (like the New Yorker) have more prestige. There is also far less room at universities for dissent (e.g. presenting an opposing scientific view or publishing investigative work).