Former CRUDES CHENG here: Alot of things could be at play which may be keeping you on the ship longer. Are you a GSE? Which underway watches do you stand? Depending on the depth on the bench will your early departure put people in a port and starboard situation or worse? Within your rate, are there any junior Sailors reporting soon? Does your ship have a deployment on the horizon and are they just keeping you for the deployment?
Have you asked to speak to your CO about his/her desicion on the why if it hasnt been adequately answered by your CoC? That conversation may help you understand the why.
And please, if you don't understand your importance and your role within the department please take some time and think about that. You're more important than you think. At least you have been deemed important enough to gain a spot at OCS...