For reference, I'm mostly talking about brand-new projects, and purely from my perspective as a former .NET dev that still spends time with the local .NET community.

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.