Why is Windows Activated?

[Xcrysdale]

Hey guys really stupid question, but upon installing Windows 10 Pro Edition after completely wiping my main drive, the OS installs already activated. I have purchased Windows 7 about 3-4 yearsa ago, and upgraded for free to Windows 10 about 1 year ago, but I'm baffled by how I'm able to get Windows 10 Pro Edition completely free every time I mess up my system and want to reinstall. Is it somehow tied to the hardware in my system, therefore knowing it's been activated before? It's genuinely confusing, and makes me curious because upon installing from USB (Media Creation handled by the Windows 10 Setup Helper on another completely different computer) it prompts me to insert a key, but instead I select "Not right now" and am presented with a list of Windows Versions I can install (Ranging from Educational to Pro - No Enterprise). Proof that I'm somehow activated has been shown below, if anyone has any insight I would love to know how this keeps happening. Thanks all!

 

 

[Shimejii]

Windows 10 is Motherboard bound. SO you can reset it and as long as you keep the motherboard it will reactivate.

[GoodBytes]

When you upgraded to Windows 10, Windows 10 took your Windows 7 key, upgraded to Windows 10 one (you can still use it to install/activate Windows 7), and linked it with your system motherboard and other specs, and/or with your Microsoft linked account.

 

When you install Windows 10, the first thing it does when you come online is communicate with Microsoft server to send your system specs and valid it with their server, if there is a match, Windows activates.