This question has been answered several times by myself and others, but

Comment on Apollo Moon Landing Hoax – Scientific Evidence by jfb.

This question has been answered several times by myself and others, but it basically boils down to 3 things, mainly:

1. $$$$$$$$$$$$$$$. Everything boils down to money, as in, too goddamned much of. Manned lunar missions are fiendishly expensive because of the mass requirements. You’re not just sending people, you’re also sending all the air, food, and water required to keep them alive for the entire trip. I think the ratio is for every kilogram of payload, you need 9 kilograms of propellant, or something like that. Yes, there have been advances in materials, electronics, and communications that allow us to shave those mass requirements by a couple of hundred kilograms or so, but that’s still a lot of mass to shift. That means big rockets with big engines, which in turn mean big money.

Although, with the development of the SpaceX Falcon Heavy launchers and Dragon spacecraft, it might be possible to jump-start a small manned lunar program at a “reasonable” cost (for suitably loose definitions of “reasonable”; it’s still going to be an obscene amount of money, but less obscene than the SLS, if it ever gets built and flies). It would take multiple launches per mission (the old Earth-Orbit Rendezvous method that was considered for Apollo but ultimately rejected because of the mass requirements), but given the economies of scale SpaceX is hoping to achieve, it may bring the cost down to something that wouldn’t get laughed out of committee.

Provided the Texas delegation in Congress doesn’t kill CCDev or the follow-on programs. SpaceX doesn’t have the financial clout of the established aerospace companies that are angling for the SLS money, and most congresscritters are smart enough to go with the big money.

There are always plans to return to the Moon, but there’s never the money to actually accomplish those plans. See the Constellation program for a stellar example. The Shuttle and the ISS have sucked up so many manned spaceflight dollars for so little return that many in Congress and the general public question the justification for the manned program in the first place.

2. The Apollo program was a child of the Cold War. Hell, the space program as a whole was all about the superpowers showing off their lovely intercontinental ballistic missiles to each other. The Soviets had beaten us with the first satellite and the first manned flights, so beating the Soviets to the moon was a national priority. Once Armstrong and Aldrin successfully landed, support for the program in Congress quickly collapsed because the major goal had been accomplished. We won. Add to that the fact that the Soviet manned lunar program got started late, was poorly managed and badly underfunded, and that the N1 booster had a nasty habit of blowing up almost immediately after liftoff, there was simply no way the Soviets could match us. There was no need to go back again, and Congress managed to cut the last two flights.

3. From a scientific perspective, unmanned missions offer far greater bang for the buck. For the cost of a single manned mission, you could pepper the surface with unmanned rovers similar to what we sent to Mars. Indeed, missions like Clementine, Lunar Prospector, and LCROSS have returned a wealth of data that rival or surpass what we got from Apollo, for far less money, and far less risk to human life. Technology has advanced to the point where we don’t need to send people to do basic exploration; in fact, it’s wastefully expensive to do so. Instead of launching a huge capsule with lots of wasted space, water, food, and air, you build a small spacecraft with as many scientific instruments as it can carry. Much less mass, meaning much smaller rocket, and it doesn’t ever have to come home, meaning you don’t need to send the propellant to get back again.