It’s a long trip and there’s nothing to do there.

Wait, I might be confused with Western Australia.

Something not happening is not really a fact or something that requires explanation. Nobody walking on the moon is the default state of the moon. It's normal. A moon walk would in fact be big news because it's a very exceptional and massive exception to the state of reality. Then not walking on the moon afterwards is just return to normal.

Going there was purely political. There is nothing there and no good reason to go back once it fell out of public favor. On top of that, they didn’t keep good records as to how to make the rockets, so we don’t have the ability to just remake the rockets we used back then and would instead need to reinvest into making new ones. It’s obscenely expensive with no discernible benefits.

What kind of explanation are you looking for?

As well as the required technology, it was political will during the cold war that drove the manned landing back then. That political will hasn't been there since: no-one is really interested in being second on the moon just for the sake of it.

And technological advances have, if anything, made manned missions less necessary if we want to investigate particular subjects: robots and remote scanning can do far more these days without the need for boots on the ground.

Because there really is little reason to do it.

Its much cheaper and safer to collect scientific data with probes and remote operated vehicles.

So many people and technical parts need to work together properly, and there's the risk of one person or one piece failing, that may cause total failure and costs millions of bucks plus several human lives.

It was difficult then to find the right people and the needed technology - and it is difficult today.

There are countless places on earth that I'm sure have seen as few or even fewer visitors - desolate rocks in the middle of the ocean, remote mountain peaks, areas made inaccessible due to vegetation or climate. Going to any of them would be infinitely cheaper and less difficult than going to the moon, and yet no one has, because unless you have a particular reason to spend the money and effort to get there, why would you?

I'm sure there are scientists who'd love to run some sort of experiment on the moon, but aside from that it's a lot of work for not much beyond bragging rights, and the US kinda got those by getting there first. There isn't a lot of political will to spend billions right now to test things on the moon that we can reasonably simulate here much cheaper with computers.

The logical answer is that we just don't need to anymore. The conspiracy answer is something along the lines of that they saw something they didn't like and don't want to go back.

We've learnt everything we can from the Moon. It's a needless expense to keep going there, unless it's to set up a Moon base for missions to Mars.