Microsoft moving to .Net Core means all developers will ultimately need to move that direction. ST has to pull that bandaid off at some point.
Linux is a far more diverse environment than is Windows. I see no way to replicate all possible operating systems and configurations of software and hardware without getting a product out into beta.
.Net Core and Kestrel will mitigate that to a degree which is why this is even possible.
ST needs to continue innovating on its products to stay competitive in the market.
All of these factors are inherently at odds with one another. One has to keep up with the tools that are being provided, must keep the product stable, must innovate to retain and attract customers, must open up new markets, and must keep existing installations stable.
ST must delicately balance these elements. I think .net core represents a good way to do this in a way that reduces risk for its current clients. My guess is that a large chunk of the code did not have to be rewritten to make this move.
I had to double the size of my SM server for the memory requirements of the latest major release. I am excited that Linux is less expensive to run than is Windows and I might be able to get my server cost back under control with this move. I have been happy with the performance and stability of my other .Net Core Linux-hosted applications.