Microsoft ended support for the driver SecDRV.sys (used by SafeDisc) due to severe security vulnerabilities. As a result, Windows 10 and 11 run original RCT discs natively.

) are DRM-free and don't require a disc, original physical copies require a "No-CD" workaround to run without the disc in the drive. Primary Method: Registry Edit

The second reason was Digital Rights Management (DRM). Publishers feared piracy (understandably so), and the simplest way to prevent someone from copying the game folder and giving it to a friend was to require the physical disc. The game executable would "phone home" to the CD drive at launch; if it didn't detect the specific table of contents of the original disc, the game wouldn't start.