Why would you use Windows 7 when official support for it ends in 1 year?
Because it’s cheaper, easier to use with the Loader Program, takes less resources, and Microsoft support is unnecessary for using it solely with the Loader Program.
Why buy a product key in the first place? You can run Windows 10 just fine with no product key legally, you just wont have access to all of the operating system's features.
Please show us where Microsoft states that is the case and what states what features are excluded and included.