Solaris is not free software and the free software forks never gained much traction. Plus it is now also associated with Oracle which brings along a lot of extra distrust, particularly given how litigious they are.
Oracle used excuse, that it's current OpenJDK license (GPLv2) is incompatible with license, used by Google's runtime (Apache 2). If Google re-licensed it's Java implementation under GPL, some of arguments, used by Oracle lawyers (code reuse and patent (?) violations), would have been void, and arguing about reuse of APIs would have been a lot harder.
Of course, this does not really matter, because the whole lawsuit is just excuse for power games between corporations. Oracle's goal wasn't about Java licensing, it was about gaining some degree of control over emerging Android ecosystem.
cgroups, Jails, and Zones all suffer from having to cover an immense surface area. Contrast with VMs, which only require managing a few, significantly simpler interfaces. There are definitely differences in quality, but they all use a similar approach.