Yeah there is more software available on MacOS or Windows in this field but you are way way way overstating your case.
The GPP is absolutely not overstating the case. I love Linux and open source, but it really isn't ready for audio recording and MIDI processing, let alone the myriad of other apps and plugins required for effects processing and mastering. I would be extremely surprised if there are any serious audio professionals using Linux as a DAW.
As for the rest of us: inspiration can be difficult to find. When an idea for a song strikes your chosen platform and toolset must be ready to record perfect audio with low latency now. No configuration, no messing about. Load host, press record, start playing. Anything else is a compromise and will hamper your creativity.
OS X and and Windows allow this to happen with very little configuration. The plugins are available, both free and paid. Linux does not. It may do in the future with host like Bitwig being made available (soon ...), but until that day it's Mac or Windows for consistently repeatable high quality audio work.
Peace,
Andy.