Why might an application designed for one operating system fail to run on another?

An application designed for one operating system may fail to run on another due to unique system calls that are specific to each operating system. System calls are the programming interface that allow applications to request services from the operating system's kernel. Different operating systems have their own set of system calls, each with varying functions and behaviors. When an application is built, it relies on the system calls provided by the operating system it was designed for. If that application is moved to a different operating system that does not recognize those specific system calls or has different system calls for similar functionalities, the application will not be able to execute properly.

This difference in system calls is a primary factor for incompatibility, leading to potential runtime errors or outright failure to launch. While there could be other reasons for an application failing to run on a different OS, such as hardware incompatibility or CPU architecture differences, the unique system calls directly pertain to the way the application is programmed to interact with its native operating environment.