Why do some logging modules accept duplication of lower error levels?

Question

Journaling

For example, there is a handler that writes log messages with emerg level and below to emerg-log.txt. There is also a handler that writes log messages of the error level and below to another error-log.txt file. It turns out that if an emerg-level error occurs, emerg-log.txt and error-log.txt will be the same, duplicate data will appear.
Why, for example, winston and, probably, many other modules for logging use this approach with "top-down duplication", if you can call it that?