Why Ransomware Attacks only Targeting Windows Users?

No, that is a wrong interpretation of how ransomware works. Ransomware, most of them were developed with Windows in-mind, using standard Windows APIs to operate their encryption process. However, it is well known to infect Linux and MacOS with the Wine package installed. Wine is a translation layer to run Win32 apps in Linux and MacOS, installed by advanced users for them to continue Windows applications in their platforms.

However, the chances of a Wine-package to get infected by ransomware is very low, since advanced users don’t use the Wine translation layer as a root user. Only a root user can have a full control in the Linux and MacOS environment.