Microsoft announced the free upgrade in January 2015 with the goal of getting as many users on the then-new Windows 10 operating system as possible. At the time, Microsoft said that the upgrade would only be valid for one year, but the free upgrade option never ended. In early 2020, Microsoft said it was not going to stop doing this for the time being. So it is not clear why they decided to stop it now?
Source: Windows Ends Installation Path for Free Windows 7/8 Upgrade
Source: Windows Ends Installation Path for Free Windows 7/8 Upgrade