It was designed to fail
Solaris is fantastic on SPARC but an absolute pile of dog shit when you try put it on top of equally mediocre x86 hardware and market share of x86 version clearly reflected it, there's simply no reasons why would anyone choose Solaris x86 over alternatives. Open source dog shit is still a dog shit. Solaris 9 for x86 was never ever released long before Sun bite the dust, that says a lot about demand for it. ZFS ? Maybe. Dtrace ? There's one for Linux if you need it.