Microsoft continues to phase out Windows 7 and 8.1:
Out with the old, and in with the new. Microsoft yesterday stopped providing Windows 7 Professional and Windows 8.1 licenses to original equipment manufacturers (OEMs), including its PC partners and systems builders. This means that, as of today, the only way you can buy a computer running Windows 7 or Windows 8.1 is if you can still find one in stock.
Two years ago, Microsoft stopped selling Windows 7 Home Basic, Windows 7 Home Premium, and Windows 7 Ultimate licenses to OEMs. Now Windows 7 Professional and Windows 8.1 are also out of the picture, leaving Windows 10 as the only remaining option, assuming you want a PC with a Microsoft operating system.
This is Microsoft's way of slowly phasing out old operating systems. The Windows Lifecycle chart for sales doesn't have an end date for Windows 10, since that operating system doesn't have a successor.
(Score: 1) by nobu_the_bard on Wednesday November 02 2016, @01:05PM
Windows 7 stopped being supplied to retailers in 2013. Windows 8 stopped being supplied in 2015. You may still be able to find copies but supply is no longer being replenished, so the longer you wait the harder it will be to find affordably. Try to make sure you get a retail copy, not an OEM license; the OEM licenses tie themselves into the hardware you use, so they are less portable. The retail licenses are more expensive but less hassle if you intend to use them for a long time. I'd advise also trying to get a Windows 7 Pro license to get it reasonably feature-complete.