China's effective A2/AD paying dividends.
On top of compounding mistakes regarding shutting down F-22 manufacturing, designing short legged, cramped F-35s etc with complex variabts, LM and every vendor in value chain milking off profits as they are obliged to the shareholders and not the country, declining manufacturing in general, all adding up to insane costs.
Meanwhile, China built J-20 to be longer range, bigger aircraft that has bigger room for future upgrades and is being upgraded. US played a lot of strategic cards wrong with all the advantages in the world.
If they want something cheaper and effective solution, perhaps a dual engine bigger airframe similar to F-35 with lots of overlaps, would be cost efficient in so many ways.
But the industry and lobbyists will push for a new cash cow.
While China is upgrading J-20s and starting to blur the lines between 5th and 6th gen fighters. China's 6th gen will iterate from J-20, US is iterating from F35/22. We've reached a point where it can be argued that US will need to make a bigger jump than China when moving into 6th gen air platform. Something inconceivable just 10 years ago