Hi,
Gypseagirl. Welcome to the board.
I find it tragic that we basically abandoned the promise of Apollo for so long. But, speaking as an American, as a country we have a pretty short attention span, and the social upheavals of the '60s, Vietnam, etc., not to mention a President (Nixon) who had no interest in space all helped turn us back on the path to following up the landings with more lasting missions and development.
And, as others have already said, it comes down to money - getting into space is expensive - and money = political support, and no national will = no political support. We are struggling to redevelop the heavy-lift and man-rated launch infrastructure which will follow the Shuttle and enable a slower, but steadier and longer-term, exploration program.
And others
do want their flag on the Moon. The then-Soviets tried very hard but their heavy-lift booster kept exploding back during the Apollo era. Now, the Chinese have big ambitions and lots of cash, including developing their own robust manned space program and manned expeditions to the Moon.
As far as the radation "belts", they were extensively investigated during the decade leading to the first Apollo landing. (The Apollo missions actually used trajectories which ensured the crews spent minimal time transiting them; see Bob Braeunig's
terrific explanation of this if you're interested.) The models developed by NASA before, during, and after Apollo are standards of the industry and are verified every day by the continuing operation of
many commercial, military, and civilian spacecraft which transit or operate continuously in the Van Allen belts.
But I was really wanting to know why nobody has been there since. BTW, yes I do believe WWII did happen 
