Why isn't Windows 10 free to distribute?

This has been making me wonder for a while.

1.) If Windows 10 is now "free"; 2.) and if MS's revenue stream is now based on advertising; 3.) and if therefore it's in MS's interest to have Windows 10 installed on as many PCs as possible---then why is MS still "licensing" Windows and verifying---a la Windows Genuine "Advantage"---against your hardware)??? What the flip do they care if I copy Windows 10 to a new computer or a 100 new computers? Isn't that what they want? I don't get this at all.

You'd think they'd want to distribute Windows 10 with all the ease of a Linux Distro. What am I missing?