A vain punt by LM for the Japanese coproduction contract. the USAF is already looking ahead to the next generation fighter - the Penetrating Counter Air (PCA) fighter with the range and performance to take on China.
With the F-35 in series production it is unlikely that LM would also get the next major contract - particularly with their performance with the F-35 - and Boeing is hungry for something to replace the F-15/F-18.
Boeing's Newest Next-Gen Fighter Concept | Ares
Similarly the USN is also ramping up for the next generation.
https://en.wikipedia.org/wiki/F/A-XX_Program
Why would the Japanese instead buy into a hybrid of a 40 year design which is proving astronomically expense to upgrade and a 30 year old design bomb truck which is dismally failing to perform and proving so expense to build that even putting the F-22 back into production is starting to look attractive?
Fool me once, shame on you; fool me twice, shame on me......