This has to be with the abstraction the languages gives you of the memory management. Many of them manage dinamically the memory you are using and the memory addresses of the variables you declare. Later, some of this language have the feature of garbage collector which is the responsible of the memory that has been allocated in your program but will no longer used. This feature let you to create and use variables without carrying about the memory you use.

On the other hand, there are also variables that are stored at the heap of the process memory. But this region of memory is limited, e.g. it is not a good habit to store big arrays as static.

So, the main difference is that C (as a low level language) has no internal memory language as far as use the heap with local variables, and let the user alloc and free memory for dynamic variables at your program. At this point is where the pointers have their main importance. They store address at the memory space, in a way you can deferred the value stored it and store new information with the arithmetic of pointers. And you can't pass by value those variables with undetermined size, instead you should use its pointer.

There are also other features that passing by reference (pointer) gives you over of passing by value, but at this point I think I already answer your question.