From reading that review process, the main reason Debian banned it seems to be that in their view you can not use Debian together with SSPL licensed software an

From reading that review process, the main reason Debian banned it seems to be that in their view you can not use Debian together with SSPL licensed software and be compliant with the conditions of SSPL. The guideline (DFSG) does not specify what to do in this situation, which is acknowledged in the discussion, so the reason for banning the license comes down the fact that inclusion would not benefit the goal of the project. The OSI seems more focused on the OSD 9, which depend on the interpretation of Services as derived works. This a different discussion and a very large grey zone. The review request did however get withdrawn we won't get a definitive answer.