Why unix is not open source?

there is an open-source project based on a heavily modified and specialized Unix code-base, this is called OpenSolaris from Sun Microsystems but this was discontinued when Oracle acquired Sun

however the open-source efforts has continued with an OpenSolaris fork called OpenIndiana and similar distributions based on the illumos kernel which remains theonly available open-source descendant of the UNIX System V, Release 4 (SVR4) code base developed by Sun and AT&T in the late 1980s..

OpenSolaris was developed as a combination of several software consolidations that were open-sourced subsequent to Solaris 10, and was meant to be the community-driven effort to provide the future code-base of Solaris 10 onwards..