You can build Tizen apps in .Net now I imagine they're working to improve compatibility across all Tizen devices. Samsung is also now a member of the .Net foundation
Assuming they implement the entirety of the .NET APIs then a developer would have to invest very little to get on their platform. One would hope anyways.
aside from frequent platform changes, and the fact that very little amount of users use Tizen, I believe C# is a much better environment for app development. C# has much better tooling around it (remember how long it took to have a stable android studio, let alone have it in the first place)
They already went through Meego APIs, replaced by Bada OS C++ APIs, replaced by C and Enlightenment APIs, alongside HTML5 apps.
As a developer I would be weary to invest any resources in so unstable OS design.