Windows 10 is incompatible with two forms of annoying and invasive DRM, SafeDisc and some versions of SecuROM, which prevents a handful of older games from running on fully-updated gaming PCs.
You might have heard of SafeDisc and SecuROM before, and that's because both of these DRM implementations are notoriously bad, often preventing legitimate users from playing their games. As Windows 10 is incompatible with this DRM, however, some games such as Grand Theft Auto III, The Sims, Flight Simulator 2004, and Battlefield 1942 won't run at all.
According to Microsoft's Boris Schneider-Johne, Windows 10 deliberately doesn't support some variants of SecuROM used on games released between 2003 and 2008. This is because SecuROM is so "deeply embedded in your system" that it becomes a security risk, potentially forming an entry point for malware and other viruses.
SafeDisc, on the other hand, relies on system driver 'secdrv.sys' that is no longer present in Windows 10. The DRM itself hasn't been supported by its developers for a few years, but Microsoft kept supporting the required driver up until Windows 8.1. Windows 10 removes support for this driver, again most likely due to security issues.
While removing support for two forms of invasive DRM is good for users' security, it does prevent gamers from enjoying some older games on Microsoft's latest operating system.
There are still some options for gamers wanting to play affected games, including installing a no-CD crack or re-purchasing the game without DRM through a store like GOG. However this can be fiddly and annoying, especially considering these games worked in previous versions of Windows.
Considering Microsoft's strong stance in favor of securing their operating system and protecting users, without official patches for the games in question, it's unlikely they will be officially supported from Windows 10 onwards.