Yikes, do you mean Windows Subsystem for Linux? I really appreciate MS folks putting in the effort to try something new, but WSL is close to worthless. I tried it a while back and could not get basic services to work. And why would you want Windows OS around if you just want to run Linux?

First, I really do appreciate what you are trying to say - that proprietary software is where the money is. It also could be that most of the time, there really isn't a reason to share source code. I've built lots of software for companies large and small. Most of that software is for automating some very specific business process, or making some machine configuration work that no one else in the known universe would ever want anyway. The only developers who that code has value to will work at or for that company. It's not that it is secret, it's just a snowflake. In many cases the budget was so small, that the application wasn't tooled to run anywhere else but on that customer's existing infrastructure, so it would take more time to make that code open-source ready. BTW, open source code generally (but not always) is much higher quality than what I see in most proprietary software because it is going to be reviewed by lots of others and there is often an expectation that that code work on multiple platforms.

Also, when you use absolutes, like "All significant open source development is done by folks ... cashing a paycheck" you are guaranteed to be wrong. It is also disingenuous to people who actually are out there scratching an itch... and to all those developers who started by scratching and itch and finding customers or companies to pay them to keep scratching that itch.

Commercial UNIX never had that problem, I was dual booting between Windows NT and Linux during my university degree.