It's called "having fun" to lots of people. That is living a life, one where you do the things you are passionate about.

writing code is an excellent way to improve your skills... Of course some people don't care about improving themselves. They usually end up leeches on society as they end up on social security during the next round of layoffs. Whether that code you write is part of an OSS project or not is of course another question, and a valid one. Myself I write things for personal use. Though I have contributed to OSS in the past, I've pretty much stopped doing that (beyond hanging out in support forums) for a variety of reasons.