Microsoft is now all-in on Windows 10. The company has stopped selling OEM licenses of Windows 7 Professional and Windows 8.1 to manufacturing partners, effectively restricting all new systems to Microsoft's latest operating system.
Microsoft's partners have had some time to prepare for the end of Windows 7 and 8.1 OEM sales as the dates have been available in Microsoft's lifecycle fact sheet for years. Most companies don't even bother selling products pre-loaded with older versions of Windows, particularly as most consumers want the latest software anyway.
The end of sales for Windows 7 Professional comes a full two years after sales ended for Windows 7 Home Basic, Home Premium and Ultimate. Windows 8 sales ended a few months ago, and Microsoft has been quick to end sales of Windows 8.1 shortly afterwards. Currently, Windows 10 does not have an end of sales date.
While you can no longer purchase systems with Windows 7 or Windows 8.1 pre-installed, Microsoft is still supporting both operating systems for many more years. Windows 7 is currently in its extended support phase, and will receive security patches until 2020. Windows 8.1 is in mainstream support until 2018, after which it will enter the extended support period until 2023.
There is some good news for those that desperately want a Windows 7 Professional or Windows 8.1 license: some retailers like Newegg are still stocking official OEM licenses. However, once stock runs out, that's pretty much it for older versions of Windows.