They are GNU/Linux. The problem is 1. Silica is proprietary (although you aren't technically forced to use it to create a Sailfish application if you don't want to) and 2. the architectures of the prebuilt applications don't match those of 99,999% of regular computers, so you wouldn't be able to run them either way.

Then, 3. why would you want to do so in the first place? The only 'killer app' I can think of that's missing on all other platforms and on desktop GNU/Linux is Pure Maps, but as far as I know, it isn't optimised for usage on anything other than a mobile device.