No, linux support is not the only new feature. Read the change logs, it's thousands of huge improvements everywhere.
Yes, there is other nice language features but obviously 15 years of Framework code base has probably put up guard rails around those sharp edges.
My point still stands, I can't imagine most companies green lighting .Net Framework -> Core conversion if they can't switch to Linux. If you are stuck on Windows, you have probably developed all the tooling to deal with Windows so it's all sunk costs.
Getting access to things like Kestrel (breaking out of IIS jail) is way more critical. Also, self contained deployments mean you can stop shipping magical blessed machine images around. It's not even about the performance. It's about having technology that doesn't actively hate you.
Also they aren't the only ones, same applies on the Apple ecosystem, only those around Mac OS and OS X early days actually manage to find sensible documentation.