I've listed a couple reasons below. I got out because I didn't like my orginal MOS and got off active duty and switched jobs in the reserves.
Believe it or not, Lt, Captains, and Majors have some of the highest deployment rates.
Here is why:
1. A typical enlisted soldier will stay with their initial units anywhere to four to six years. So in that period of time that unit could possible deploy for at most 36 months (Assuming a 1:1 ratio of deployment to dwell). So your average soldier will deploy at most for three years. Most likely they will do four years and get out. This means about 3 years at a deployable unit and maybe one to two deployments.
2. A typical officer has a four to six year contract. An officer will spend about their first tour with a deployable unit (normally two to three years). After their first tour they go to a "B" billet or transfer to another deployable unit or some try to be accepted into the SF community. The B billets are normally non-deployable, but because combat operations take a lot more officers to run than normal peace time operations, the military has to staff those requirements (like BCT night current operations officer (Captain)). Officers who are in their B billet and think they are going to have two to three years home with the wife and kids are normally the ones asked to fill these requirements. So lets say they do a year in country and then go back and finish up their B billet. The next tour is going to be with another deployable unit. So it is very possible that if you did 9 years in as an officer you could have up to five or six deployments.
3. Enlisted soldier get off of active duty and then go in the reserves and only join a reserve unit or guard unit if they want to. If they don't, they most likely will not get called up unless they have a unique skill or MOS. Officers get off active duty and go into the reserves and either have to join a unit or face the high likelihood of being called up to fill one of those staff positions mentioned above. So they get off of active duty as soon as they can and accepted that they'll have one more deployment in the reserves before they can resign their commission.
Also, a lot of Officers are tired of going to Iraq. If there was a better rotation where units did an Iraq tour and then an Afghan tour, a lot of officers would probably stick around.
Finally, there is also a large segment that is getting out because they don't like the mission. They didn't join up to spend seven months in Iraq doing civil affairs or training the Iraqi Army. They feel this is not what they signed up for and that they have done their duty and aren't sticking around to do more of the same. This is a HUGE problem for the Artillery community.
http://www.npr.org/templates/story/story.php?storyId=90200038