Why does Unity ship official (preview) packages with in-editor-compilation-errors?

Upgraded DOTS.
Now this: 15 times something similar to this: “Library\PackageCache\com.unity.entities@0.9.0-preview.6\Unity.Scenes.Editor\BuildStepCreateResourceCatalog.cs(18,51): error CS0619: ‘BuildStep’ is obsolete: ‘Replace with BuildStepBase. (RemovedAfter 2020-07-01)’”
Trying to fix it by hand leads you down some obscure rabbit hole where you START by overwriting virtual functions of types that are defined in preprocessor directives.

Why? Unexpected behaviour is one thing, but this […]!!!

It looks like this package is not compatible with newest version of the Editor. As stated by this error, BuildStep became obsolete only after 2020-07-01 and 2020 versions are still in Alpha. You are essentialy using preview package (so like beta or early-access however you want to call it) with alpha version of editor. I’m not surprised something doesn’t work

is not only 2020 also 2019.3.9 has the same issues like 15 errors and haven’t figure out how to fixes yet. I tried following errors suggestions like replacing BuildStepBase with BuildBase but at the end editor crashed.