Why do I stutter is the wrong question!  If you are eager to change, you ask "how" instead of "why?"  People who stutter have a "structure" to their stuttering; oftentimes it is very predictable.  An example would be when a server comes up to my table, I take a breath, look away, say several "ums," and then force out the word "h-h-h-hamburger."  That is how I stuttered.  How I stutter explains specific words and situations we routinely stutter on.  Why is a culdesac- you drive in circles- and HOW is the highway to change.