Because, half a century later, it's not any cheaper to do it than it was then.
Cost per kilogram delivered to LEO:
Saturn V (used for the Moon landing mission): $8,250
Falcon 9: $2,700 (price for an expendable launch)
BFR (hypothetical, in development rocket): $500
Just because it's cheaper to take the bus downtown doesn't say anything about the cost of airfare to another continent.
IIRC: Saturn V could put 100k pounds in lunar injection. The first SLS will be around 50k, the Falcon Heavy around 40k.
Layer versions of the SLS, should we choose to spend more tens of billions developing them, will eventually have Saturn V capabilities.
The BFR (as planned) will be the largest capacity rocket ever made. Putting 300k+ in low earth orbit. It’s designed to be refueled in orbit, so essentially it’s lunar/mars injection orbit payload caisvity is 300k+.
It’s also designed to be fully reusable, unlike the Falcon series that only reuses main boosters. So it’s claimed to be far cheaper than them, and they are already the most affordable rockets ever made.
The SLS is designed to be crushed and melted like a beer can after every launch, which is why it will cost $2B+ per launch.
Back in 1973, the total cost of the Apollo program reported to Congress was $25.4 billion. By far the most expensive parts of the mission were the Apollo spacecraft (the Command Modules, the Lunar Modules) and the monstrous Saturn V launch vehicles. A single Saturn V launch cost up to $375 million in 1969 — or, in today’s money, a few billion dollars.
In 2009, NASA looked back at the cost of the Apollo program in its entirety, and arrived at a figure of $170 billion in 2005 dollars (or around $200 billion in today’s money). Compare these costs to modern day space travel, where companies like SpaceX charge just $133 million to launch a spacecraft to the International Space Station. The Falcon Heavy, which will be comparable to the Saturn IV, will be in the same price region.
https://www.extremetech.com/extreme/186600-apollo-11-moon-la...
SLS: $15,000
Falcon Heavy: $700
The truth was it’s stack had massive launch capacity, over 200,000 lbs. but it was almost all used up by lifting that space plane. A higher launch rate was never really possible. The solid boosters weren’t reusable without a huge amount of work, and the shuttles needed lots of maintainance between flights.
The BFR is designed with theses lessons in mind. It’s fully reusable and it’s seconf stage should be way more efficient. But we will have see how much maintenance it will require between flights.