However, the base it runs on - Mer - is open source, and there is an alternative open UI (Glacier UI). Unfortunately this further limits the applications that can run on it.
By the way, the phone runs a real Linux distro. There's Wayland, OpenSSH, bash, systemd (ugh...), RPM's, and a ton of good old commandline software like htop, tmux, python, - heck, even gcc if you feel like rebuilding the kernel :) Native apps are built with Qt & QML. There's very little NIH.
There's also support for Android apps. Many of the apps from F-Droid run OK, and even lots of commercial stuff.
Oh, and the phone is pretty fantastic for all the normal everyday things, like being an actual phone.
It's somewhere on my TODO list :) I make a "f*ck you Krzysztof" app for every new phone OS I get: there's one for J2ME, Android, now gotta learn myself some QML... Krzysztof is not very amused.
Willingness and ability are different things. Samsung never tried to push Tizen on mobile phones.
Samsung put itself in a position where the company simply cannot walk away from Google, at least in the mobile space (Tizen is actually pretty "mainstream" in smart TVs and wearables). Market shares are pretty much set at this point, and no alternative mobile OS based on linux has a chance to become mainstream, no matter the size of the company backing it. That doesn't stop a small company like Jolla from delivering viable products though, since they don't need to keep Google happy.
IMHO, with Russians being paranoic about western "spying" and Russians committing their code to upstream, it's likely that there will be something to see in a couple of years.
It looks to me that all Sailfish devices that have ever been available are not compatible with 3G/4G US carriers (but some are compatible with 2G).
It seems that if anyone in the US wants to seriously use Sailfish, they need to flash a community port of Sailfish to a US-sold Android device. Not a huge deal - it looks like a few manufacturers are actively supporting this ports (e.g. for the Fairphone 2): https://www.fairphone.com/en/2015/10/22/jolla-community-work...
UPD:
Jolla -- company behind SailfishOS (ex-Nokia people) https://jolla.com/about/