I heard this story as well. But in the end they picked something else they had and could make. I think the original idea was to start with the same as what went to the moon and build on that. At one point we made several thousand of something like them. They found they could not build that anymore, and it was not as good as stuff they could do, so they redesigned to something else that they could. That is as far as most people take that story.
In fact most 'stories' and 'news' is like that. The SLS is known to be in a congress sub committee hot potato game. So that there are different versions floating around of what happened and is happening is not surprising. Teasing out the 'truth' of what happened is not always easy. As many have interests in distorting it, or just remember wrong.
There were not thousands of F-1 engines manufactured. There were a bit over a hundred manufactured between flight and test models.
The whole "we can't make them anymore" meme has a tiny kernel of truth but it's been blown way out of proportion the more it's been repeated.
When the F-1 was manufactured a lot of the actual assembly of parts was done by hand. That meant Rocketdyne's engineers and machinists had a lot of tribal knowledge that was lightly or partially documented at best or not documented at worst. NASA and Rocketdyne maintained all of the designs and documentation and knew everyone involved in the engine manufacturing.
In the early 90s a lot of these Rocketdyne people were interviewed [0] and asked to review F-1 manufacturing techniques as part of the Space Exploration Initiative [1]. Restarting production of the F-1 would have been practical but more expensive than the alternate plan to go with an SSME derivative.
While the F-1 is an impressive engine it has downsides. It's enormous and heavy. The Saturn V's first stage (S-1C) was 10m in diameter while the Space Shuttle's external tank was 8.4m in diameter. The Shuttle's ET was going to be the core of the proposed SEI rocket (and SLS). With a 8.4m tank diameter it would be more difficult to mount more than two F-1s.
With only two engines it would be more dangerous of a vehicle for manned missions as a flame out in one engine could be disastrous. It would also make it more difficult to throttle the engines for different launch profiles. Moving to a larger core would have required all new manufacturing infrastructure, flight qualification, and unknown follow-on issues.
Tl;dr The F-1 was an awesome engine but not perfect or even desirable for all purposes and the "we can't build them" meme is stupid.
In fact most 'stories' and 'news' is like that. The SLS is known to be in a congress sub committee hot potato game. So that there are different versions floating around of what happened and is happening is not surprising. Teasing out the 'truth' of what happened is not always easy. As many have interests in distorting it, or just remember wrong.