I don't know. Even small defensive nations like Israel , south korea and Canada have dual engine jets. I think its just cope.
Japan has no proper army they still have them
First, the US does not consider the F-16 to be 'inferior' to the F-15. Not sure where you got that from, but never mind.
When I was active duty, I went from the F-111 (Cold War) to the F-16 (Desert Storm). During the Cold War, the F-111 was a strategic bomber capable of reaching Russia proper. Then during Desert Storm, the F-111 became the fighter-bomber capable of going anywhere in Iraq. When I got orders to deploy to DS, I got calls from former F-111 teammates and we talked about what our respective squadrons would be doing in Iraq. Suffice to say that we knew before deployment that the F-16 would be doing more in terms of versatility than the F-111 could. That is not a knock on the F-111 but even though both jets can go anywhere in Iraq, that the single engine F-16 can turn around faster than the F-111 made the F-16 the better choice for most combat missions.
Anyway...Doctrines compels hardware, whether it is development and/or purchase. The corollary is that the hardware available compels doctrines. It is a push-pull relationship. Twin engine platforms like the F-15 and F-111 compels a doctrine of deep incursions into enemy territory, air and/or ground. If the F-16 was not available, what would you do? Limiting the F-15 usage to only border defense? Not likely. But if you have a limited budget, then with the combination of budget and hardware availability, you would have no choice but to purchase the F-15 and limit its usage via doctrines. Your budget would have allowed more F-16s but unfortunately, it does not (yet) exist, and your defense needs is urgent, so you buy what is available and develop your doctrines from there. Do you see the problem here?
On the other hand, for US, given our national wealth, we can afford to make doctrines leads development, meaning we outline what we want to do
THEN we build the hardware to suit. The US and the Soviet Union can afford to do this. Most of the rest of the world -- cannot. Not on a consistent basis. Now that the SU is no more and Russian aviation is a shell of its former self, that leave US and China as the two aviation powers that can execute on the formula: doctrine before development. The rest of the world buy
THEN come their doctrines.
Israel is wealthy enough and has an ally -- US -- that are willing to support it in spite of global opinions. Plus, given their national defense needs, they can afford to buy the F-15
THEN develop their doctrines. Am not going to get into geopolitical and moral debates on the US-Israel alliance. I will leave the forum's Israel members to do that. But I will say that from a military aviation power perspective, Israel needs the F-15 more than the F-16, and they got both, and that made them the dominant regional air power they are today.
During the Cold War, the US and the SU developed their doctrines, built to match, then sold to our allies. The F-4 is an example. That jet was sent to everywhere. Today, it is different. We talked to our allies, formulated a common doctrine, then
COOPERATIVELY build. The results are the F-16 and F-35. Of course, the US and China will build and keep our respective superior platforms, the F-22 and J-20. Each serves unique doctrines.
In terms of utility, the F-16, in my opinion, is the best platform out there. For example...If you have a border crisis, threatening the enemy's capital deep inside his territory is an option. For most of the world's countries, the F-16 can do that
PLUS capable of carrying enough ordnance to support frontline troops fighting at the border. The F-16 with a centerline fuel tank and an all-air config is a capable patrol platform from inland to marine territories. An F-16 with a centerline fuel tank can carry more bombs to make a quick dash to the battlefields. The jet's flexibility is well known and that is why it is still in production today.