I have never quite understood why so many powers (the United States, Canada, Japan, etc) have lined up to try and buy F-35s. Every plausible enemy our countries

I have never quite understood why so many powers (the United States, Canada, Japan, etc) have lined up to try and buy F-35s. Every plausible enemy our countries could square off against have extremely old technology (or no technology to speak of). In fact, I would be prepared to argue that slightly updated F-15s are superior to anything that any plausible enemy could attack us with. Am I wrong? If so, help me understand why!!