It seems that the release process only releases .jar files and not other maven artifacts as .tar.gz and .zip. This can be seen for example here in the releases repo:

https://nexus.onap.org/content/repositories/releases/org/onap/policy/api/policy-api-tarball/

Last release of these artifacts date back to May.

Comparing it with the snapshots repo:

https://nexus.onap.org/content/repositories/snapshots/org/onap/policy/api/policy-api-tarball/

These non-jar artifacts are produced with every merge.