Microsoft's Advanced Threat protection is part of Windows 10. And while the company would love for everyone to keep up and run the latest version of their operating system, there are still plenty of people running older versions of Windows. In order to protect them, Microsoft will be extending availability of Advanced Threat Protection to Windows 7 and Windows 8.1.
From the middle of this year, you will be able to add Windows Defender ATP Detection & Response (EDR) to Windows 7 Service Pack 1 and Windows 8.1. In their announcement, Microsoft said the move is to help "customers achieve the best security possible on their way to Windows 10."
This is a good thing. Many businesses struggle to move their entire fleet to a new OS with legacy and bespoke applications often built or specifically configured to fit an OS. By adding this protection, Microsoft supports those customers and avoids a situation, such as when last year's WannaCry attack broke out, where they have to quickly retrofit patches and protective measures to older operating systems.
By doing this now, they can alleviate some of the pressure of pushing out a quick fix later.