but... where's the source? Those are all closed, proprietary programs. They might be fine in their own right, but they are not free software. Audacity is free software, as is Ardour.

The better answer to this question is probably that Mac OS X is not the best platform to run free software on, just like Microsoft Windows is suboptimal at best. Given that those platforms are closed and proprietary this is not that surprising. If you want to run free software, start at the bottom - the kernel. It is not like there is a dearth of choice when it comes to running free kernels after all.