I've never met a software developer, musician, or artist who didn't have a side project of some sort in addition to their "day job".
You're putting software developer in the same category as musician or artist?!?
Which one of these things doesn't belong?
Writing software is considered a creative act.
I was one of the participants in the Department Of Labor study that decided that,
Jobs that are more than 50% creative are exempt from overtime pay requirements. Software engineering, unless you are job-shopping it as a contractor is considered more than 50% creative. Which means that if you are salaried, you don't get overtime pay.
Personally, when I write software, it's being processed in the part of my brain that processes music. Meaning I literally can't write software if there's music playing at the same time.