BLU-27 in Japanese Tech Tree

I knew USSR and USA employ napalm in their service and uses it quite often and many nations either did not uses it to begin with or only withelding the license to use but not actually having it in their inventory.

That being said, where does the BLU-27 that is present in F-15J comes from and why does it not exist in planes before F-15J? is there a history that I missed here?