Linux

A ton of them apparently come from regional pricing, or from keys purchased by businesses. Windows offers volume licensing where you can buy bulk keys at a steep discount, basically. The business might not use all of them, and then they turn around and resell them. That's technically against the terms of the license, but afaik Microsoft has never bothered to enforce that.

I've also heard people will take the Windows keys off of older OEM towers and resell them. I have no idea how true that is, but it would also be against their terms.

It's not exactly likely, but Microsoft could probably just deactivate all of those keys at once if they decided to.

Microsoft doesn't give a shit to stop it, because they profit off your data. They give it away for free themselves. They don't care how you get it if you are on their system, and then they do everything they can to trap you. They don't make their profit from key sales.

You aren't taking anything from anyone. It's just an algorithmically generated activation.

This is so easy it's kinda nuts, and there are multiple methods to activate. All you should need for Windows these days.

https://massgrave.dev/

Those are good questions that I don't have the answers to. Although from the research I did at the time it seems most likely they were purchased with regional pricing in a lower price region.