Packagers grab a source ZIP and build from there, but by default GitHub doesn't include submodules in source ZIPs, so grabbing the source ZIP from a release won't build correctly out of the box.
The source ZIP on a release should include the vcpkg submodule (and any other submodules, but vcpkg is the only one so far) so that the program can be built from the source ZIP directly.
Packagers grab a source ZIP and build from there, but by default GitHub doesn't include submodules in source ZIPs, so grabbing the source ZIP from a release won't build correctly out of the box.
The source ZIP on a release should include the vcpkg submodule (and any other submodules, but vcpkg is the only one so far) so that the program can be built from the source ZIP directly.