[inerte]

Let's say you write a Python program that outputs Javascript. It could be considered a "compiler". Or let's say that you write your own language, which outputs to other 3 or 4... there's also compiling involved. A compiler doesn't need to output assembler. Even if every compiler did that, features of the language would result in different execution code.

For example, PHP's variables can be a string of any size, or a number, or an object, and you can change its type while the program is running. The compiler doesn't optimize the code execution as easy as, say, in Java. You can not allocated the minimum amount of memory that will store the variable values, for example.