The person you're replying to already gave you an example of someone who does exactly what you're saying is impossible!
> There are many commercial JDK/JVM offerings that are closed source and survive very well with their "secret sauce" (usually GC related), such as Azul's Zing JVM.
How does that work? Even if code is GPL if you own it you can do what you want with it. That includes licensing it to someone under a _different_ licence. Being available under the GPL does not mean it can't also be available under another licence, such as a proprietary one. Which is what is done in this situation.
> but it does redefine the choices to "clone software entirely" or "fork existing software and share changes" .. it removes the option of "fork existing software and DON'T share changes"
None of this is true.
Oracle could not do that for all of OpenJDK today unless OpenJDL has a super weird CLA that signs away ownership of the code because they do not own all of the code.
Copyleft can't prevent other people from making a clone of your software, but it does redefine the choices to "clone software entirely" or "fork existing software and share changes", it removes the option of "fork existing software and DON'T share changes", i.e. benefiting from the open source nature of the project without giving those same benefits to others.