DoD does not need nor want to retain physicians. They will pay for your training, get some years out of you and then gladly watch as you move on to the civilian world.
@pgg is right.
If you end up marrying someone who also has a solid income then you may stick around longer.
If your cost of living is super low based on your upbringing and lifestyle choices you may stick around longer.
If your self worth is derived equally between family, recreation and occupation you may stick around longer if #1 or #2 is met.
If your specialty is one of the few that has a high volume/complexity in the military you may stick around longer if #1-3 are met.
Plus there are about 4,251 other things to consider.
No problem either way whether people stay or go...just be honest with yourself so you don't make yourself and everyone around you miserable.