What interested me most is that Pardus project had its own packaged manager called PiSi, which was then adopted by Solus.

I bet Pardus project had their own reasons to adopt the apt system and rely on Debian volunteers for all packaging support. As the OS is largely maintained by a government institution, I'd imagine it doesn't have the large userbase as Debian does.

There are also some other cool projects made for Pardus, for example Zemberek, a spell checker for the Turkish language that uses natural language processing for Libreoffice and Openoffice: https://github.com/ahmetaa/zemberek-nlp