I understand the stated reasons and disagree with their conclusions. It seems like a lot of extra work on the part of the Zig developers to have to reverse engineer undocumented interfaces. There is potentially extra work for the Windows developers if they want to change their private implementation details that Zig programs are now relying on. And in the case where the lower level APIs are missing features implemented higher level APIs, Zig has to either reimplment the functionality themselves or not have the same level of support for Windows features that normal Win32 apps have. A concrete example is looks like Zig programs can't open serial devices:
The reasons are clearly stated in the issue you have linked.