The problems with OpenSolaris
Even before Oracle summarily killed off OpenSolaris, I didn't find it very attractive. I had two serious general problems with it.
The first is that Sun didn't seem to make any effort to make OpenSolaris into a useful and usable distribution. Instead what you got (at least from an outside perspective) was periodic snapshots of a development tree, something like Debian testing or Fedora Rawhide. This made perfect sense from Sun's perspective, but I didn't have any particular interest in building things on sand.
(When Sun offered OpenSolaris support, the support period was too short to be useful to us.)
The second is that OpenSolaris has always depended on Sun's goodwill, and not just for continual source updates. The OpenSolaris source code is incomplete; both building a binary system from source and important bits of system functionality (like a good chunk of the NFS code) required using closed source components that Sun generously gave people for free. If Sun had wanted to cripple OpenSolaris usage in practice, all it ever had to do was change that and we would have been left with something that was about as directly useful as 4.3 BSD Lite.
(Part of this illustrates how big a debt the open source world owes to gcc, which in many ways is the unsung foundation of both the *BSDs and Linux. Yes, today we have open source alternatives. Today.)
These problems meant that I couldn't consider OpenSolaris to be an insurance policy and viable alternative in case Sun went crazy with Solaris. Although Sun might not be able to retract the source code, they could go just as crazy with OpenSolaris and make it unusable if they ever felt like it.