I'm a little surprised that China was willing to offer that. Limiting American production of high-tech weapons for the next decade is an incredibily potent advantage, and it's not worth giving up for just a few years of high-end semiconductors.
However, I'm not surprised that the Americans didn't take up the offer. They are very poor at planning for the long term, and in American politics, giving up stances that were adopted in the name of national security is very difficult to justify. Maybe they're already thinking of ways to either smuggle rare earths or to take the civilian allocations and give it to military contractors.
Lockheed Martin is supposed to have enough for F-35 production up until the end of this year. After that, they said that they expect the US government to give them priority for future supply.