You haven't needed Visual Studio to build .net projects for a long time, project files are MSBuild files.
Now you don't have to edit them as often (wildcards for files), they're easier to edit by hand (because they contain almost no clutter) and there are also command line tools to edit them (like dotnet add package).
<Compile Include="**/*.cs" />
I was doing this back in the .NET 3.5 days.But nitpicking aside your point is well taken, the developer experience is far better with dotnet core.
It's just that building from Visual Studio is by far the most convenient method.
Before there was a project format, callable with devenv command line tool.