Why? Not everything is free and open source. In fact, most of the operating systems used outside the "general-purpose" Linux realm are not (e.g. OS400, z/OS, z/TPF, AIX, Solaris, NonStop, QNX, vxWorks... even Windows Server).

That said, if you're really interested, HP offers free hobbyist licenses for non-commercial use of OpenVMS, with access to the OS and compilers and usable on real hardware or SIMH.

Could you please send me the link where it says that I can get the hobbyist license. I want to give it a try.

Sure: https://www.hpe.com/h41268/live/index_e.aspx?qid=24548

Last time I tried (few years ago) I was contacted via email by an HP guy who asked me what architectures I needed licenses for, and then sent me a private FTP login to download all the files.

Some links to get you started:

http://labs.hoffmanlabs.com/node/23

https://www.wherry.com/gadgets/retrocomputing/vax-simh.html

If you want to emulate on SIMH I suggest you compile the latest from source (it's on GitHub).

I got licenses for my MicroVAXen some years ago. I haven't powered either of them on in a long time though...

FYI, hobbyist licenses expire after a year. You'll have to get new ones. Still free.

There was a project to reimplement OpenVMS under the GPL, http://www.freevms.net/ - I think the project has stagnated, though, the last commit in their git tree seems to have happened about two years ago.