I've been using .NET Core for new projects since it first came out, and I think it's important to remember that a couple years back .NET Core wasn't really stable enough for production use (in comparison to .NET Framework). The original project files were in a different format, you often had to fight the tooling, and important libraries like Entity Framework were missing key features. Despite that, the fact that Linux was a target platform made the whole thing worth it.

Core 2.0 came out mid 2017, and in my mind I still wasn't sure .NET Core had cooled down enough to port applications from .NET Framework. 2.0 turned out to largely be stable enough for production, but there wasn't really any way of knowing that without watching it for a few years.

We've only just gotten to the point where moving an important production code base to .NET core actually feels like the correct thing to do. I'm sure there will still be some hurdles involved, but at least there won't be too many landmines.