It is fairly understandable that existing proprietary DAWs do not run on Linux, given the rather small (but growing) share of the desktop market that Linux has. However, when surveying the landscape of "popular operating systems", we find:

• older versions of Windows: plagued by abysmal stability and appalling security
• newer versions of Windows seem stable but still suffer from security problems
• OS X: an amazing piece of engineering that is excellent for audio work but only runs on proprietary hardware and still lacks the flexibility and adaptability of Linux.

Security matters today, and will matter more in the future as more and more live or semi-live network based collaborations take place.

Let's contrast this with Linux, an operating system which:

• can stay up for months (or even years) without issues
• is endlessly configurable down to the tiniest detail
• is not owned by any single corporate entity, ensuring its life and direction are not intertwined with that of a company (for a contrary example, consider BeOS)
• is fast and efficient
• runs on almost any computing platform ever created, including old "slow" systems and new "tiny" systems (e.g. Raspberry Pi)
• is one of the most secure operating systems "out of the box"

More than anything, however, Ardour's primary author uses Linux and wanted a DAW that ran there.

Having written a DAW for Linux, it turned out to be relatively easy to port Ardour to OS X, mostly because of the excellent work done by the JACK OS X group that ported JACK to OS X.
Although OS X has a number of disadvantages compared to Linux, its ease of use and its presence in many studios already makes it a worthwhile platform.