Why is compiled code not portable from one platform to another?

Compiled code is not portable between platforms primarily due to differences in hardware architecture, operating systems, and system libraries. When code is compiled, it is translated into machine-specific instructions tailored for a particular environment, which may use different data types, memory management, and system calls. As a result, the same source code may require recompilation and potential modifications to run on different platforms. Additionally, dependencies on platform-specific features or libraries can further hinder portability.