I use Linux for music because I use Linux for software work. As such I did not run Windows nor Mac for years and years.
If you were not already using Linux for software work (or some other compelling reason either as a professional like yourself, or hobbyist like me) and approached a computer as a non-technically savvy musician, there would be no compelling reason to choose Linux, let alone FOSS.
I'm am not all all down on Linux for making music or I wouldn't be doing it myself. I love it! But everyone here knows it takes some work and a significant investment of time to get to that place where it seems easy. Audio engineers or bedroom producers who are not into Linux can either choose to make 10 new tracks or poke around jackaudio.org/faq. And that's just the start of the curve.
The only people who think making music on Linux is easy or accessible for average musicians are people who enjoy using Linux already.
"Are there any big artists that use FOSS software?" Even if the question were rephrased to "Linux" instead of FOSS, I think the the answer will be no, not yet.
Someday it will happen, and we'll have 100 new users here saying "I can't get sound to work!".