Also, from what i saw, nobody is actually in a rush to "move" to .NETCore, most big shops still rely on .Net Framerwork , i still do some occasional work on a project which is using .Net Remoting :)
I know plenty of people that would love nothing more than to be up to date and to start using .NET Core, but many of them rely on certain libraries that simply aren't there yet. I know a load of Umbraco devs that are eager to make the jump, but until their CMS supports it, they're kinda stuck if it's a dependency.
People are hold back because of deprecated tech and because no one touches a running system without need. And maybe that black matter developers just do not know yet ;).
I've not met a single .NET dev that doesn't want to use .NET Core. Hell, if anything, a lot of them would love the opportunity to use .NET on a Unix system, and to use established tooling not available on Windows. The problem is that the tools they use aren't ported yet.
Umbraco is a key example, as the most popular .NET CMS in use today. It's a great CMS, but we're at least 1-2 years away from a .NET Core implementation, and probably even longer if we're hoping for a first-class Postgres/MySQL backed implementation. Until then, as you've rightly said, there's no need to switch to .NET Core.