This is probably an intentional oversight by Microsoft. Nobody wants to have to deal with Windows 7 anymore, so leaving an option for people to upgrade for free

This is probably an intentional oversight by Microsoft. Nobody wants to have to deal with Windows 7 anymore, so leaving an option for people to upgrade for free allows the continued obsolescence of that OS (yes, I know the official support was discontinued, but it still looks bad on Microsoft if a bunch of Windows 7 devices suddenly get exposed to an 0-day).