Logging is a fundamental technique in programming. Sometimes it's the single available diagnostic tool. No surprise there're a lot of different logging libraries. They provide logging to different kind of targets most of them you never heard about, dozens of log categories (like "warning", "serious warning", "almost error", "critical error", "the end of the Earth"), comprehensive configurations and output formats, vertical takeoff (I'm sure I remember one such log-library), etc. And I'm sure there're projects that really need all those features. Who doesn't need them writes their own logging.
