One of the major aspects of Solaris demise was that it fell victim to the anti-cannibalization efforts by the extremely politically strong SPARC division inside

One of the major aspects of Solaris demise was that it fell victim to the anti-cannibalization efforts by the extremely politically strong SPARC division inside Sun. That bound the Solaris fate to the [rapidly falling] fate of the Sun SPARC and prevented any serious investment into the development of the x86 version. As Solaris was falling more and more painfully behind in support of popular x86 hardware a running joke ca. 2002-4 from the Solaris dev guys was - to have an instance of Linux kernel with its drivers running inside the Solaris instance and use that Linux instance to proxy requests to the various otherwise unsupported by Solaris hardware.