If it really happened then why hasn't it happened again? If it was so easy to do back then, why haven't we been up there again with all the technology we have now. With the tech we have nowadays we would be able to build a structure of some kind on the moon to allow prolonged stays for research but instead we stay in the comfort of our close orbit in a space station to conduct research
Why don't go back there? Because there's nothing there, it's simple as that. The composition of the Moon is 50% oxygen (I'm talking about the atom, not the molecule O2), 20% silicon and 13% iron, the rest is traces... All of this is abundant on Earth so why bother going up in space to get it? And what use do you have in building a base on a satellite with no atmosphere, almost no gravity, and too far from Earth to get precise and fast data over time? They went there because sending men in space was revolutionnary, it meant "YEAH WE CAN DO IT!". But there's absolutely no use in sending men to the Moon. However there's a use in sending them to Mars, and NASA is preparing a 200-person team to populate Mars currently, and they put a lot of budget into it.
It wasn't easy. NASA would love to do more manned missions to the Moon, to speak nothing of eventual larger-scale-unmanned and manned missions to Mars and Venus with the hope of laying the groundwork for colonies, but they're expensive. A not-insignificant portion of the nation's GDP went to the moon landing, and it only happened because it was sold as a means of beating the Russians in the space race. The fact that we can operate the very complicated space stations is to no small degree because of what we learned in the moon program.