For, many, many, many reasons. That would be two huge programs. First you would have to rebuilt the very expensive, very costume Apollo stuff again. And then you have to do a very expensive modernization.
Things are simply not done now, as they are done in the 60s. The manufacturing methods are completely different. The supply chains are complete different. The organization of NASA is completely different. The politics of Congress is different. Society is completely different.
The Apollo hardware was a product of its time and its context. You couldn't build it exactly as they did even if you tried.
Why would you rebuild an analog computer from the 60s when you can get 100x more computation power in a 1 cent microchip? Or better solar panels? Or better communication.
And once you are making fundamental changes anyway, why be linked to choices from the 1960s still? Just because Apollo was successful doesn't mean it was a 100% flawless and perfect program.
There are some parts of Apollo tech that are reused in various ways, and lots of data from Apollo is used. But more then that doesn't make a lot of sense. The Orion Heat-Shield is pretty much like the Apollo Heat-Shield. But even in that simple case, they had to do a lot of work to replicated that. So the idea that 'make it like Apollo' was a great money-safer is simply wrong. The opposite is true, looking backward towards Shuttle and Apollo is holding the space program back.
But Apollo was also a different goal and a different architecture. Artemis wants to have people one the moon for weeks. Apollo did only a few days. The capsule is far bigger. The lander can land far more weight, in case of Starship, about 100t. They are planning a rover that people can live in for 30 days.
There are exceptions. For example, the F-1 engine was considered for modernization multiple times. When NASA built the SLS, a F-1 based Saturn V like rocket was considered. And in fact, such a rocket did actually score better then the Shuttle based pre-SLS when they did the evaluation around 2011.
However it was not picked because of various political power plays from different people, both inside NASA and inside congress. The Shuttle is what dominated NASA for 30 years, and Shuttle interest matter, Apollo interest don't. That's why SLS looks like the Shuttle.
But even that is wrong as it would have been even cheaper to make this properly competitive, like they did with COTS. So SpaceX, ULA and other could have build what they needed. This was actually considered but was politically not viable at that time.
By now you can use the Raptor engine, its just leagues better then even a modernized F-1. So whats the point?
Orion was built for the early 2000 Bush moon mission and has survived because of politics. Nobody sane would build it that way again. But its not politically possible to kill it. So for 20 years it has stuck around in search of a mission. Its design really constrains the architecture you have to use.
- "When NASA built the SLS, a F-1 based Saturn V like rocket was considered. And in fact, such a rocket did actually score better then the Shuttle based pre-SLS when they did the evaluation around 2011."
I think you've mixed up engines: the one SLS was evaluating around 2011 was J-2X, a derivative of Saturn's hydrogen engine J-2. Not the main stage kerosene F-1. The upper stage J-2X was intended for was cancelled and downgraded.
You can look various talks and papers from back then. NASA made a lot of 'studies' back then. One of the SLS engineers in a talk basically said 'I can not do another vehicle study, I have done to many'.
They were evaluating a RP1 based first stage with a large gas-generator kerlox engine. In these studies they often don't use engine names directly. That of course is F-1, see F-1B on wikipedia to get some links.
Somewhere I have some reddit post that have 100s of links to all the different studies and videos on this topic. I can check tomorrow if I can find those posts.
A modern J-2 and F-1 would basically make a modern Saturn V.
Of course from my perspective all these studies are not gone have the right outcome because they aren't actually asking the right question in the first place, but that's another matter. But the results of the study didn't actually matter because congress basically mostly just decides it anyway.
There was some cavitation issues in the "injector plates" of the F1 where the LOX and kerosene mixed with was resolved by drilling holes in it until it went away - there was no method to the pattern just drilling holes in a pattern until it went away.
Also each F1 differed slightly from the engineering design as they found issues and fixed it en-situ.
In short copying 1960's designs today is not going to work.
https://www.youtube.com/watch?v=GYtDBi-Xf9o