Remember when Sun abandoned the workstation market (thus cutting off its developer base), then killed Solaris-x86 (thus cutting off what its developer base had migrated to), then brought it back but killed it off again a few years later because they'd literally _forgotten_ the outcry the previous time? (And then gave their salesdroids a bigger comission on each Solaris X86 seat sold than the customer paid for the license?) I guess it really does take a direct meteor strike to kill off a dinosaur.
OpenSolaris was always a Sun internal political thing. The Sun Civil War a decade back was between the once-unified "Sparc/Solaris" block and the "children of Java" (which included openoffice, looking glass, Sun's windows guys... Yes Sun had a Windows faction, which arose from the "Windows JDK" folks but later included the "OpenOffice has more deployments on Windows than anywhere else" guys). Java was always bigger than Solaris, but Sparc and Solaris were where the political power was in Sun and they killed anything that was a threat to them, keeping Java on a tight leash that seriously neutered its potential. That's why Java and such weren't open sourced for so long, the Sparclaris guys squashed it (Danese Cooper's entire job at Sun, for 6 years, was fighting against this). But when Bill Joy went crazy Sun bought co-founder Andy Bechtolsheim's startup that sold Opteron servers and Andy made 'em port Solaris to the Opterion. That split the Sparclaris faction down the middle.
The real tipping point seems to have been the Windows guys getting massive payments from Microsoft (for shilling for SCO during that FUD mushroom cloud):
Money is power in a company like that, and when the rise of Opteron left Solaris isolated they struck back by forcing Solaris open source (kicking and screaming) to politicaly neuter them (and as payback for the Solaris guys had done to Looking Glass).