Why is it that most conventional applications are incapable of copying live memory from a computer system?

a. They're not incapable. It's easy to capture memory.
b. Because memory is constantly shifting. The mere fact that you are copying the memory causes it to change.
c. Because direct access to system memory requires a kernel-mode procedure call. Most applications only have user-mode access.
d. Because system memory is not part of the regular file system.

c.