The question is more like why would you run Win7 on a Threadripper? You still have a few days to get the upgrade free (https://www.microsoft.com/en-us/accessibility/windows10upgrade). Frankly, if your reason to stay with Win7 is older game compatibility, I'd think about either dual-boot (recommended) or running a virtual machine inside Win10 (more trouble than it's worth).
There is no reason you cannot run Win7 on Ryzen/Threadripper, but you will eventually run into compatibility and driver issues.