I think the problem here is people use BAZELISK_BASE_URL because they forked the official repository and probably made some custom changes. Falling back to the official download is not what we expected.

Custom changes should not have the same version number as the official releases. So falling back to offical URLs only produces 404, which is expected.

The assumption is wrong. In one project we maintain a version internally with our tweaks and we keep the internal version align with the main public version (e.g. 6.0.0).

Even if we do not align the version strictly, I think it's still reasonable people map their internal version to an arbitrary public version (e.g. internal 4.0.0 -> public 6.0.0). It's wrong to assume 404 will definitely happen.