A lot of
Maven archetypes put this in for you as for a very long time Log4j is just what you used. For any new projects I now rip this out and replace it with Logback and Sl4j.
You can read more
http://logback.qos.ch/reasonsToSwitch.html
http://logback.qos.ch/
http://www.slf4j.org/
Note that all of these 3 projects have the same primary author. But the latter 2 were created to correct issues in the former. There is no reason to continue using log4j (no longer under active development) on any new projects.
Also sl4j is a logging abstraction layer it is not a logging framework, it is used together with a logging framework (like logback or log4j).