Because in a company setting at least, you will soon discover that you need more than file-based logs in the specific format some coder defined for his pet proj

Because in a company setting at least, you will soon discover that you need more than file-based logs in the specific format some coder defined for his pet project. So, you start logging to a database which is easy enough and then you start writing some simple templating code so that different logalizers can work on the logs etc. And then you discover that your logging is slowing down the whole application as more users are added and so on. In the end, you implement a subset of log4j, just worse. What you should have looked at is one of the lighter logging libraries and use slf4fj to switch them out if you need more.