He probably figures he wouldn’t be welcome there, but mainly all he cares about is his death care legislation. Also, he got stung for that photo op scheme at Dover last week, so he doesn’t want to risk any bad “seeking photo op” press again, and he figures if he can’t get a photo op out of it, why bother?
Also, he probably heard Dubya was going there and was afraid he’d be upstaged in the nethusiasm the troops would surely show for Dubya versus the polite but cold greeting nd stares he’d get.
Maybe he just doesn’t want to get photographed playing golf this weekend?