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...
I feel many times if a person is told the "why" behind the reason it will put everything in perspective.
Looking at some of the items you brought up I have seen the same brought up as to why a person couldn't go to a "C" school, or take leave at a specific time. The same command would immediately remove any female from the ship that popped up pregnant without regard to the the effect on the watchbill or anything else even though they could stay on the ship for several months, due to this my LT didn't disclose her pregnancy for close to 8 weeks as she didn't want to get removed prior to an inspection we were having.
If a command can get by without someone who just finds out they are pregnant they should be able to get by without a person who has another opportunity.
To quantify "immediately" depending on the CO that could be a few weeks, or being cut TAD orders that day and off the ship.