Doctors have board exams. Lawyers have bar exams. Financial professionals have their own set of exams. Electrical and mechanical engineers have professional engineer exams.
The difference is that they're standardized, so the prep industry caters to passing those exams more so than passing the interviews.
Software engineering is far from standardized because the subject matter is far too varied, so instead companies handle their own type of exams customized to their needs.
There is also a cottage industry around interview prep for lawyers, doctors, and other professions. It's just not well known because it's extremely expensive relative to spending a couple hundred bucks (if that) on Leetcode. It often takes the form of expensive 1:1 coaching that starts in the hundreds of dollars and can easily enter five figures. Students from wealthy families frequently have private coaches for this.