A lot of people get the CFI to build hours, that's great as long as you provide good instruction. Some people don't need that because they have a plane or access to a plane/hrs/a job where they can do the same. Some people say they don't want to be a CFI because they don't want the responsibility, don't want to have to teach someone, etc. I'd be wary of these people, as airlines look for future captains that have these traits and qualities. By no means that does that require a CFI, but these are poor reasons to avoid it.