It's really difficult to get a government to spend millions of dollars on a new primary weapon when there's no big wars, arms races, or real necessity for a new primary.
Look at the F22.
It costs billions of dollars, it was supposed to be the new big thing. They can barely justify maintaining a squadron of them. And it turned out to have a serious design flaw. And there's pretty much nowhere in the world where it's really required for service.
Like Canada is buying 5th gen fighters. For what purpose? We could just buy F-18Es and be just as happy about it lol
Stealth? Don't need it in -40
Single engine? Not a good idea in -40
Multi billion dollar investment? Well at least you know for a fact we're gonna ride them till they fall out of the sky.